#include <bits/stdc++.h>
using namespace std;
const long long inf = 1000000001;
const long long maxg = 4444444444LL;
vector<long long> g;
void recurs(int d, int len, long long z) {
  if (d == len)
    g.push_back(z);
  else {
    recurs(d + 1, len, z * 10 + 4);
    recurs(d + 1, len, z * 10 + 7);
  }
}
long long a[1000];
long long f[100];
long long fact(int n) {
  if (n > 50) return inf;
  if (f[n] != 0) return f[n];
  if (n == 1 || n == 0) return f[n] = 1;
  return f[n] = min(inf, n * min(inf, (fact(n - 1))));
}
bool good(int a) {
  if (a == 0) return false;
  while (a > 0) {
    if (!(a % 10 == 4 || a % 10 == 7)) return false;
    a /= 10;
  }
  return true;
}
int main() {
  for (int ll = 1; ll <= 9; ll++) {
    recurs(0, ll, 0);
  }
  g.push_back(maxg);
  long long n, k;
  cin >> n >> k;
  if (fact(n) < k) {
    cout << -1 << endl;
    return 0;
  }
  long long p = 1;
  long long m = n - 1;
  while (fact(n - m) + 1 <= k) m--;
  long long s = n - m;
  for (int i = 1; i <= s; i++) a[i] = m + i;
  while (p < k) {
    for (int i = 1;; i++) {
      if (fact(i + 1) + p > k) {
        p += fact(i);
        for (int j = s - i + 1;; j++) {
          if (a[j] > a[s - i]) {
            swap(a[j], a[s - i]);
            break;
          }
        }
        break;
      }
    }
  }
  long long ans = 0;
  for (int i = 0; i < int(g.size()); i++) {
    if (g[i] <= m) ans = i + 1;
  }
  for (int i = 1; i <= s; i++) {
    if (good(i + m) && good(a[i])) ans++;
  }
  cout << ans << endl;
  return 0;
}
