#include <bits/stdc++.h>
using namespace std;
const double eps = 1e-8;
const long long lloo = 1e18;
const int oo = 1e9;
int islucky(int x) {
  while (x) {
    if (x % 10 != 4 && x % 10 != 7) return 0;
    x /= 10;
  }
  return 1;
}
int solve(int d) {
  int res = 0;
  for (long long m = 1, _b = 9; m <= _b; m++) {
    int l = 1 << m;
    for (long long i = 0, _b = l - 1; i <= _b; i++) {
      int x = i;
      int y = 0;
      for (int j = 0; j < m; j++) {
        if (x & 1)
          y = y * 10 + 7;
        else
          y = y * 10 + 4;
        x >>= 1;
      }
      if (y <= d) res++;
    }
  }
  return res;
}
int main() {
  ios_base::sync_with_stdio(0);
  int n, k;
  cin >> n >> k;
  int gt[15];
  gt[0] = 1;
  for (long long i = 1, _b = 12; i <= _b; i++) gt[i] = gt[i - 1] * i;
  int d = -1;
  for (long long i = 12, _b = 1; i >= _b; i--)
    if (gt[i] < k) {
      d = i;
      break;
    }
  if (n <= d) {
    cout << -1 << "\n";
    return 0;
  }
  int res = solve(n - d - 1);
  vector<int> v;
  for (long long i = n - d, _b = n; i <= _b; i++) v.push_back(i);
  k--;
  int pos = n - d;
  for (long long i = d, _b = 0; i >= _b; i--) {
    int x = k / gt[i];
    if (islucky(pos) && islucky(v[x])) res++;
    v.erase(v.begin() + x);
    k %= gt[i];
    pos++;
  }
  cout << res << "\n";
}
