diff --git a/storage/zeta/rs/completed/2006.rs b/storage/zeta/rs/completed/2006.rs
new file mode 100644
index 0000000..a9f6309
--- /dev/null
+++ b/storage/zeta/rs/completed/2006.rs
@@ -0,0 +1,257 @@
+use std::{
+    collections::HashMap,
+    io::{read_to_string, stdin},
+};
+
+#[derive(Debug)]
+enum Token {
+    Atom { symbol: String },
+    AddOp,
+    EqOp,
+    Num { num: u64 },
+    Undef,
+}
+
+struct Atom {
+    symbol: String,
+}
+
+struct Molecular {
+    composites: Vec<(Atom, u64)>,
+}
+
+struct Expr {
+    composites: Vec<(Molecular, u64)>,
+}
+
+// stmt := Expr = Expr
+struct Stmt {
+    lhs: Expr,
+    rhs: Expr,
+}
+
+/*
+    Lex
+    Tokenizing
+*/
+fn lex(line: &mut String) -> Vec<Token> {
+    let mut tokens = vec![];
+
+    let mut chars = line.chars();
+
+    let mut symb = String::new();
+
+    let mut tk = Token::Undef;
+
+    let mut pull_tk = |tk: &mut Token, tokens: &mut Vec<Token>, symb: &mut String| {
+        if symb.len() == 0 {
+            return;
+        }
+        let mut current_tk = std::mem::replace(tk, Token::Undef);
+
+        match current_tk {
+            Token::Num { ref mut num } => {
+                if let Ok(parsed) = symb.parse::<u64>() {
+                    *num = parsed;
+                }
+                symb.clear();
+            }
+            Token::Atom { ref mut symbol } => {
+                *symbol = std::mem::take(symb);
+            }
+            _ => {}
+        }
+        tokens.push(current_tk);
+    };
+
+    let mut flg = false;
+
+    while let Some(curr) = chars.next() {
+        if curr.is_whitespace() {
+            pull_tk(&mut tk, &mut tokens, &mut symb);
+            continue;
+        }
+        if curr.is_uppercase() {
+            if flg {
+                pull_tk(&mut tk, &mut tokens, &mut symb);
+            }
+
+            flg = true;
+            symb.push(curr);
+            tk = Token::Atom {
+                symbol: String::new(),
+            };
+        } else if curr.is_lowercase() {
+            symb.push(curr);
+        } else if curr.is_numeric() {
+            if flg {
+                if !matches!(tk, Token::Num { .. }) {
+                    pull_tk(&mut tk, &mut tokens, &mut symb);
+                }
+            }
+
+            flg = true;
+            symb.push(curr);
+            tk = Token::Num { num: 0 };
+        } else if curr == '+' {
+            if flg {
+                pull_tk(&mut tk, &mut tokens, &mut symb);
+            }
+            flg = false;
+            tk = Token::Undef;
+            tokens.push(Token::AddOp);
+        } else if curr == '=' {
+            if flg {
+                pull_tk(&mut tk, &mut tokens, &mut symb);
+            }
+            flg = false;
+            tk = Token::Undef;
+            tokens.push(Token::EqOp);
+        }
+    }
+    pull_tk(&mut tk, &mut tokens, &mut symb);
+
+    tokens
+}
+
+/*
+    Parse
+*/
+
+fn parse_molecular(tokens: &Vec<Token>, ptr: &mut usize) -> Molecular {
+    let mut comps = vec![];
+    while *ptr < tokens.len() {
+        let Token::Atom { symbol } = &tokens[*ptr] else {
+            break;
+        };
+
+        let atom = Atom {
+            symbol: symbol.clone(),
+        };
+
+        *ptr += 1;
+        if *ptr < tokens.len() {
+            if let Token::Num { num } = &tokens[*ptr] {
+                *ptr += 1;
+                comps.push((atom, *num));
+            } else {
+                comps.push((atom, 1));
+            }
+        } else {
+            comps.push((atom, 1));
+        }
+    }
+    Molecular { composites: comps }
+}
+
+fn parse_expr(tokens: &Vec<Token>, ptr: &mut usize) -> Expr {
+    let mut comps = vec![];
+    while *ptr < tokens.len() {
+        if let Token::EqOp = &tokens[*ptr] {
+            break;
+        }
+
+        if let Token::AddOp = &tokens[*ptr] {
+            *ptr += 1;
+        }
+
+        let mut cnt = 1;
+        if let Token::Num { num } = &tokens[*ptr] {
+            *ptr += 1;
+            cnt = *num;
+        }
+
+        let molecular = parse_molecular(tokens, ptr);
+
+        comps.push((molecular, cnt));
+    }
+
+    Expr { composites: comps }
+}
+
+fn parse_stmt(tokens: &Vec<Token>, ptr: &mut usize) -> Stmt {
+    let lhs = parse_expr(tokens, ptr);
+    *ptr += 1;
+    let rhs = parse_expr(tokens, ptr);
+
+    Stmt { lhs, rhs }
+}
+
+fn count_amount(expr: &Expr) -> HashMap<String, u64> {
+    let mut counter = HashMap::new();
+
+    for (mol, cnt_mol) in expr.composites.iter() {
+        for (atom, cnt_atom) in mol.composites.iter() {
+            counter
+                .entry(atom.symbol.clone())
+                .and_modify(|cnt| *cnt += cnt_atom * cnt_mol)
+                .or_insert(cnt_atom * cnt_mol);
+        }
+    }
+
+    counter
+}
+
+fn main() {
+    let mut line = String::new();
+    stdin().read_line(&mut line).unwrap();
+
+    let mut case = 0;
+    while !line.starts_with('#') {
+        case += 1;
+        line = line.trim().to_string();
+        let tks = lex(&mut line);
+
+        let stmt = parse_stmt(&tks, &mut 0);
+
+        let lhs_counter = count_amount(&stmt.lhs);
+        let rhs_counter = count_amount(&stmt.rhs);
+
+        // calculate destoryed and created atoms
+        let mut calcs = HashMap::new();
+        rhs_counter.iter().for_each(|(symb, cnt)| {
+            calcs
+                .entry(symb.clone())
+                .and_modify(|c| *c += *cnt as i64)
+                .or_insert(*cnt as i64);
+        });
+
+        lhs_counter.iter().for_each(|(symb, cnt)| {
+            calcs
+                .entry(symb.clone())
+                .and_modify(|c| *c -= *cnt as i64)
+                .or_insert(-(*cnt as i64));
+        });
+
+        let flg = calcs.values().any(|cnt| *cnt != 0);
+
+        if !flg {
+            println!("Equation {} is balanced.", case);
+        } else {
+            println!("Equation {} is unbalanced.", case);
+
+            let mut calcs = calcs
+                .into_iter()
+                .map(|(symb, cnt)| (symb, cnt))
+                .collect::<Vec<_>>();
+
+            calcs.sort();
+
+            for (symb, cnt) in calcs.iter() {
+                if *cnt == 1 {
+                    println!("You have created {} atom of {}.", cnt, symb);
+                } else if *cnt > 1 {
+                    println!("You have created {} atoms of {}.", cnt, symb);
+                } else if *cnt == -1 {
+                    println!("You have destroyed {} atom of {}.", -cnt, symb);
+                } else if *cnt < -1 {
+                    println!("You have destroyed {} atoms of {}.", -cnt, symb);
+                }
+            }
+            println!();
+        }
+
+        line.clear();
+        stdin().read_line(&mut line).unwrap();
+    }
+}