func_code_string: #include <bits/stdc++.h>   using namespace std;   template <class T>   T gcd(T a, T b) {     return b ? gcd(b, a % b) : a;   }   mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());   const double EPS = 1e-9;   const double PI = acos(-1.);   const long long LL_INF = 1e17 + 16;   const int INF = 1e9 + 10;   const long long MOD = 1e9 + 7;   const int MAXN = 20;   set<long long> goods;   long long f[MAXN];   void gen() {     for (int i = (1); i <= (int)(10); i++) {       for (int j = (0); j < (int)(1 << i); j++) {         long long v = 0;         long long st10 = 1;         for (int k = (0); k < (int)(i); k++) {           if (j & (1 << k)) {             v += 7 * st10;           } else {             v += 4 * st10;           }           st10 *= 10;         }         goods.insert(v);       }     }   }   int per[MAXN];   int used[MAXN];   void solve() {     gen();     long long n, k;     cin >> n >> k;     f[0] = 1;     int m;     for (m = 1;; m++) {       f[m] = f[m - 1] * m;       if (f[m] >= k) {         break;       }     }     if (m > n) {       printf( -1 n );       return;     }     int ans = 0;     int offset = n - m;     for (__typeof((goods).begin()) it = (goods).begin(); it != (goods).end();          it++) {       if ((*it) <= offset) {         ans++;       }     }     k--;     int top = 1;     for (int i = m; i >= 1; i--) {       int v = k / f[i - 1] + 1;       int cnt = 0;       for (int j = (1); j <= (int)(m); j++) {         if (!used[j]) {           cnt++;           if (cnt == v) {             per[top++] = j;             used[j] = 1;             break;           }         }       }       k %= f[i - 1];     }     for (int i = (1); i <= (int)(m); i++) {       if (goods.count(i + offset) && goods.count(per[i] + offset)) {         ans++;       }     }     cout << ans << endl;   }   int main() {     int t = 1;     while (t--) {       solve();     }   }   