func_code_string: #include <bits/stdc++.h>   #pragma GCC optimize( O3 )   using namespace std;   vector<long long> v;   void lucky(long long x) {     queue<long long> q;     q.push(x);     while (x < 1e9) {       x = q.front();       q.pop();       x *= 10;       q.push(x + 4);       q.push(x + 7);       v.push_back(x + 4);       v.push_back(x + 7);     }   }   int next(long long x) {     int str = 0, ed = v.size() - 1, ans;     while (str <= ed) {       int mid = str + ((ed - str) / 2);       if (v[mid] >= x) {         ans = mid;         ed = mid - 1;       } else         str = mid + 1;     }     return ans;   }   int main() {     long long x, y;     cin >> x >> y;     lucky(0);     unsigned long long sum = 0;     sort(v.begin(), v.end());     int z = next(x);     if (y <= v[z])       return cout << (y - x + 1) * v[z], 0;     else {       sum += (v[z] - x + 1) * v[z];       int i;       for (i = z + 1; v[i] <= y; i++) {         sum += (v[i] - v[i - 1]) * v[i];       }       sum += (y - v[i - 1]) * v[i];     }     cout << sum;   }   