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

storage/zeta/cpp/completed/2903.cpp

@@ -0,0 +1,9 @@
+#include <iostream>
+#include <cmath>
+
+int main() {
+    int n;
+    std::cin >> n;
+    std::cout << (int) pow(((1 << n) + 1), 2);
+    return 0;
+}