func_code_string: #include <bits/stdc++.h>   using namespace std;   int dcmp(double x, double y) {     return fabs(x - y) <= 1e-9 ? 0 : x < y ? -1 : 1;   };   vector<long long> holder;   void dfs(long long num, int i) {     if (i == 10) {       if (num) holder.push_back(num);       return;     }     dfs(num * 10 + 4, i + 1);     dfs(num * 10 + 7, i + 1);     dfs(num, i + 1);   }   long long solve(long long idx) {     long long ret = 0;     long long hold = 0;     for (int i = 0; i < ((int)((holder).size())); ++i) {       if (idx >= holder[i]) {         ret += (holder[i] * (holder[i] - hold));         hold = holder[i];       } else {         ret += (idx - hold) * holder[i];         break;       }     }     return ret;   }   int main() {     ios_base::sync_with_stdio(false);     cin.tie(NULL);     cout.tie(NULL);     ;     long long l, r;     cin >> l >> r;     dfs(0, 1);     sort(holder.begin(), holder.end());     holder.push_back(4444444444);     cout << solve(r) - solve(l - 1) <<   n ;   }   