func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     string n;     int index = 0;     cin >> n;     int l = n.length();     for (int i = l - 1; i > -1; i--) {       if (n[i] ==  4 )         index += pow(2, (l - 1 - i));       else         index += 2 * pow(2, (l - 1 - i));     }     cout << index << endl;   }   