func_code_string: #include <bits/stdc++.h>   using namespace std;   using ll = long long;   int main() {     string s;     cin >> s;     int n = s.size();     if (n % 2 == 1) {       for (int i = 0; i < n + 1; ++i) {         cout << (i < (n + 1) / 2 ? 4 : 7);       }       cout << endl;       return 0;     }     int seven = 0, four = 0;     for (int i = 0; i < n; ++i) {       if (s[i] ==  4 ) {         four++;       }       if (s[i] ==  7 ) {         seven++;       }     }     if (seven == four && seven + four == n) {       cout << s << endl;       return 0;     }     for (int i = n - 1; i >= 0; --i) {       if (s[i] ==  4 ) {         four--;       }       if (s[i] ==  7 ) {         seven--;       }       if (seven + four != i) {         continue;       }       if (seven > n / 2 || four > n / 2) {         continue;       }       if (s[i] <  4  && n / 2 - four > 0) {         s[i] =  4 ;         four++;         int x = i + 1;         while (four < n / 2) {           s[x++] =  4 ;           four++;         }         while (seven < n / 2) {           s[x++] =  7 ;           seven++;         }         cout << s << endl;         return 0;       }       if (s[i] <  7  && n / 2 - seven > 0) {         s[i] =  7 ;         seven++;         int x = i + 1;         while (four < n / 2) {           s[x++] =  4 ;           four++;         }         while (seven < n / 2) {           s[x++] =  7 ;           seven++;         }         cout << s << endl;         return 0;       }     }     for (int i = 0; i < n + 2; ++i) {       cout << (i < (n + 2) / 2 ? 4 : 7);     }     cout << endl;     return 0;   }   