func_code_string: #include <bits/stdc++.h>   using namespace std;   template <typename T>   std::ostream& operator<<(std::ostream& str, const std::vector<T>& v) {     str <<  [ ;     for (auto n : v) str << n <<  ,  ;     str <<  ] ;     return str;   }   template <typename K, typename V>   std::ostream& operator<<(std::ostream& str, const std::unordered_map<K, V>& m) {     str <<  [ ;     for (auto n : m) str << n.first <<   =>   << n.second <<  ,  ;     str <<  ] ;     return str;   }   void gen(int i, string c, vector<string>& r) {     if (i == 0) {       r.push_back(c);       return;     }     gen(i - 1, c +  4 , r);     gen(i - 1, c +  7 , r);   }   int main() {     cin.sync_with_stdio(false);     cout.sync_with_stdio(false);     int input;     cin >> input;     std::vector<string> all_n;     for (int i = 1; i <= 10; i++) {       gen(i - 1,  4 , all_n);       gen(i - 1,  7 , all_n);     }     stringstream ss;     ss << input;     string inp_string = ss.str();     for (int i = 0; i < all_n.size(); i++) {       if (all_n[i] == inp_string) {         cout << i + 1 << endl;         return 0;       }     }     cout <<  all_n           <<  :   << all_n << endl;     return 0;   }   