func_code_string: #include <bits/stdc++.h>   using namespace std;   const long long K = 10000000000LL;   vector<long long> L;   void init(long long crr) {     if (crr > K) return;     if (crr != 0) L.push_back(crr);     init(crr * 10 + 4);     init(crr * 10 + 7);   }   bool is_lucky(long long x) {     if (x == 0) return false;     while (x > 0) {       if (x % 10 != 4 && x % 10 != 7) return false;       x /= 10;     }     return true;   }   const int MAX_M = 20;   long long fact(long long k) {     long long res = 1;     for (int i = 1; i <= k; ++i) res *= i;     return res;   }   vector<int> kth_permutation(int n, long long k) {     vector<int> res(n), num(n);     for (int i = 0; i < (int)(n); i++) num[i] = i;     if (k >= fact(n)) return vector<int>();     for (int i = 0; i < (int)(n); i++) {       long long f = fact(n - i - 1);       res[i] = num[k / f];       num.erase(num.begin() + (k / f));       k %= f;     }     return res;   }   long long perm_n, perm_m;   vector<int> perm_last;   bool init_permutation(long long n, long long k) {     perm_n = n;     perm_last = kth_permutation(min(n, 20LL), k);     if (perm_last.empty()) return false;     perm_m = perm_n - perm_last.size();     return true;   }   long long get_permutation(long long i) {     if (i < perm_m)       return i;     else       return perm_m + perm_last[i - perm_m];   }   int bruteforce(int N, int K) {     vector<int> A(N);     for (int i = 0; i < (int)(N); i++) A[i] = i + 1;     for (int i = 0; i < (int)(K - 1); i++)       next_permutation((A).begin(), (A).end());     int ans = 0;     for (int i = 0; i < (int)(N); i++)       if (is_lucky(i + 1) && is_lucky(A[i])) ++ans;     return ans;   }   int main() {     init(0);     long long N, K;     while (cin >> N >> K) {       --K;       if (!init_permutation(N, K)) {         puts( -1 );         continue;       }       long long ans = 0;       for (int i = 0; i < (int)(L.size()); i++) {         long long l = L[i];         if (1 <= l && l <= N && is_lucky(1 + get_permutation(l - 1))) ++ans;       }       cout << ans << endl;     }     return 0;   }   