#include <bits/stdc++.h>
using namespace std;
int res;
int a[100], ins[100];
int IsLucky(int x) {
  for (; x; x /= 10)
    if (x % 10 != 4 && x % 10 != 7) return 0;
  return 1;
}
void Dfs(int now, int lim) {
  res++;
  if ((long long)now * 10 + 4 <= lim) Dfs(now * 10 + 4, lim);
  if ((long long)now * 10 + 7 <= lim) Dfs(now * 10 + 7, lim);
}
int main() {
  int n, m, k;
  scanf("%d%d", &n, &m);
  long long cnt = 1;
  for (int i = 1;; i++) {
    cnt *= i;
    if (cnt >= m) {
      k = i;
      break;
    }
  }
  if (k > n) {
    puts("-1");
    return 0;
  }
  memset(ins, 0, sizeof(ins));
  for (int i = 0; i < k; i++) {
    cnt = 1;
    for (int j = 1; j < k - i; j++) cnt *= j;
    int ret = (m - 1) / cnt;
    m -= ret * cnt;
    for (int j = 0; j < k; j++)
      if (!ins[j]) {
        if (ret == 0) {
          ins[j] = 1;
          a[i] = j;
          break;
        } else
          ret--;
      }
  }
  res = 0;
  for (int i = 0; i < k; i++)
    if (IsLucky(n - k + 1 + i) && IsLucky(n - k + 1 + a[i])) res++;
  if (4 <= n - k) Dfs(4, n - k);
  if (7 <= n - k) Dfs(7, n - k);
  printf("%d\n", res);
  return 0;
}
