#include <bits/stdc++.h>

using namespace std;

int solve() {
  int n, m, p;
  cin >> n >> m >> p;

  vector<int> a(n);
  for (int i = 0; i < n; i++)
    cin >> a[i];

  sort(a.begin(), a.end());
  if (a.back() > m)
    return 1;
  
  int y = -1;
  for (int i = 0; i < n; i++) {
    if (a[i] % p) {
      y = max(y, a[i]);
    }
  }

  if (y <= 1)
    return -1;

  int ret = 0;
  long long x = 1;
  while (x <= m) {
    x *= y;
    ++ret;
  }
  return ret;  
}


int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout << solve() << endl;
  
  return 0;
}