func_code_string: #include <bits/stdc++.h>   using namespace std;   int n, k;   long long ln[10000], fac[15];   int cnt, ans, suf;   int tem[15];   void input() { scanf( %d%d , &n, &k); }   void dfs(long long x) {     if (x > 10000000000LL) return;     ln[cnt++] = x;     dfs(x * 10 + 4);     dfs(x * 10 + 7);   }   void make_lucky_number() {     cnt = 0;     dfs(4);     dfs(7);     sort(ln, ln + cnt);   }   void get_my_suf(int s) {     bool used[15];     memset(used, false, sizeof(used));     for (int i = 1; i <= s; ++i) {       int u = (k - 1) / fac[s - i];       k -= (u * fac[s - i]);       u++;       for (int j = 1; j <= s; ++j) {         if (!used[j]) u--;         if (u == 0) {           used[tem[i] = j] = true;           break;         }       }     }   }   bool check_lucky(int x) {     while (x) {       if (x % 10 != 4 && x % 10 != 7) return false;       x /= 10;     }     return true;   }   void solve() {     fac[0] = fac[1] = 1;     for (int i = 2; i <= 13; ++i) fac[i] = fac[i - 1] * i;     if (n <= 13 && k > fac[n]) {       puts( -1 );       return;     }     for (int i = 0; i < cnt; ++i)       if (n - 13 < ln[i]) {         ans = i;         break;       }     suf = min(n, 13);     get_my_suf(suf);     for (int i = 1; i <= suf; ++i)       if (check_lucky(n - suf + tem[i]) && check_lucky(n - suf + i)) ans++;     printf( %d n , ans);   }   int main() {     input();     make_lucky_number();     solve();     return 0;   }   