func_code_string: #include <bits/stdc++.h>   using namespace std;   template <typename T>   using minpq = priority_queue<T, vector<T>, greater<T>>;   long long pl, pr, vl, vr;   int k;   long long inter(long long a, long long b, long long c, long long d) {     return max(0LL, min(b, d) - max(a, c) + 1);   }   int main() {     ios::sync_with_stdio(false);     cin.tie(0);     cin >> pl >> pr >> vl >> vr >> k;     long double ans = 0;     vector<long long> lucky;     for (int len = (0); len < (11); len++) {       for (int x = (0); x < ((1 << len)); x++) {         long long y = 0;         for (int i = (0); i < (len); i++) {           if ((x >> i) & 1) {             y = y * 10 + 4;           } else {             y = y * 10 + 7;           }         }         lucky.push_back(y);       }     }     sort((lucky).begin(), (lucky).end());     int n = ((int)(lucky).size());     for (int i = (1); i < (n - k); i++) {       int j = i + k;       ans += 1.0 * inter(pl, pr, lucky[i - 1] + 1, lucky[i]) *              inter(vl, vr, lucky[j - 1], lucky[j] - 1);       ans += 1.0 * inter(vl, vr, lucky[i - 1] + 1, lucky[i]) *              inter(pl, pr, lucky[j - 1], lucky[j] - 1);       if (k == 1 && pl <= lucky[i] && lucky[i] <= pr && vl <= lucky[i] &&           lucky[i] <= vr)         ans--;     }     ans /= 1.0 * (pr - pl + 1) * (vr - vl + 1);     cout << fixed << setprecision(11) << ans <<   n ;   }   