func_code_string: #include <bits/stdc++.h>   using namespace std;   long long l, r, ans;   vector<long long> lucky;   void lu(int f, int s) {     string x =   ;     for (int i = 0; i < f; i++) x +=  4 ;     for (int i = 0; i < s; i++) x +=  7 ;     do lucky.push_back(atoll(x.c_str()));     while (next_permutation(x.begin(), x.end()));   }   int main() {     cin >> l >> r;     for (int i = 0; i <= 10; i++)       for (int j = 0; j <= 10; j++)         if (i + j <= 10) lu(i, j);     sort(lucky.begin(), lucky.end());     int j, k;     j = k = 0;     while (lucky[j++] < l)       ;     j--;     while (lucky[k++] < r)       ;     k--;     ans += lucky[j] * (min(r - l, lucky[j] - l) + 1);     if (lucky[j] == lucky[k]) return cout << ans << endl, 0;     ans += lucky[k] * (r - lucky[k - 1]);     for (int i = j + 1; i < k; i++) ans += (lucky[i] - lucky[i - 1]) * lucky[i];     cout << ans << endl;   }   