#include <bits/stdc++.h>
using namespace std;
bool isLucky(long long n) {
  if (n == 0) return false;
  while (n) {
    if (n % 10 != 4 && n % 10 != 7) return false;
    n /= 10;
  }
  return true;
}
long long fact[20];
long long cnt(long long k, vector<long long>& n, long long curInd) {
  if (n.size() == 0) return 0;
  long long sz = n.size();
  long long cur = 0;
  while (fact[sz - 1] <= k) {
    k -= fact[sz - 1];
    cur++;
  }
  long long res = 0;
  if (isLucky(n[cur]) && isLucky(curInd)) res = 1;
  n.erase(n.begin() + cur);
  curInd++;
  return res + cnt(k, n, curInd);
}
int main() {
  fact[0] = fact[1] = 1;
  for (long long i = 2; i < 20; ++i) {
    fact[i] = fact[i - 1] * i;
  }
  long long n, k;
  cin >> n >> k;
  if (n < 20 && k > fact[n]) {
    cout << -1 << endl;
    return 0;
  }
  k--;
  long long res = 0;
  for (long long len = 1;; ++len) {
    for (long long i = 0; i < (1 << len); ++i) {
      long long num = 0;
      for (long long j = len - 1; j >= 0; --j) {
        num *= 10;
        num += ((i >> j) & 1) ? 7 : 4;
      }
      if (num > (n - 15)) goto next;
      res++;
    }
  }
next:;
  vector<long long> lastN;
  long long start;
  for (long long i = n; i >= 1 && i >= (n - 15); --i) {
    lastN.push_back(i);
  }
  start = lastN.back();
  reverse(lastN.begin(), lastN.end());
  cout << res + cnt(k, lastN, start) << endl;
  return 0;
}
