func_code_string: #include <bits/stdc++.h>   using namespace std;   long long ans, l, r, j, cn, ii, ix, p, N = 4e3;   vector<long long> A;   long long pww(long long a, long long b) {     long long r = 1;     for (long long i = 1; i <= b; i++) r *= a;     return r;   }   void gen(long long i, long long p) {     long long r = 0;     for (long long k = 0; k < p; k++) {       if (i & (1 << k))         r += pww(10, k) * 7;       else         r += pww(10, k) * 4;     }     A.push_back(r);   }   int main() {     cin >> l >> r;     while (cn < N) {       ii += 1;       long long pw = pow(2, ii);       for (long long a = 0; a < pw; a++) {         gen(a, ii);       }       cn += pw;     }     p = l;     while (A[j] < l) j++;     ix = j;     for (ix = j; A[ix] <= r; ix++) {       ans += A[ix] * (A[ix] - p + (ix == j ? 1 : 0));       p = A[ix];     }     ans += A[ix] * (r - p + (ix == j ? 1 : 0));     cout << ans << endl;     return 0;   }   