func_code_string: #include <bits/stdc++.h>   using namespace std;   vector<long long> all;   void backtrack(long long x, int cnt4, int cnt7) {     if (x > 1e10) return;     if (cnt4 == cnt7) all.push_back(x);     long long nxt = x * 10 + 4;     backtrack(nxt, cnt4 + 1, cnt7);     nxt = x * 10 + 7;     backtrack(nxt, cnt4, cnt7 + 1);   }   int main() {     std::ios_base::sync_with_stdio(0);     cin.tie(NULL);     cout.tie(NULL);     int n;     cin >> n;     backtrack(0, 0, 0);     sort(all.begin(), all.end());     cout << *lower_bound(all.begin(), all.end(), n);     return 0;   }   