restructure zeta/** to storage/zeta/**

storage/zeta/cpp/completed/27866.cpp

@@ -0,0 +1,10 @@
+#include<iostream>
+
+int main() {
+    std::string s; int N;
+    std::cin >> s;
+    std::cin >> N;
+    std::cout << s[N-1];
+    
+    return 0;
+}