#include<bits/stdc++.h>
#define int long long
using namespace std;

signed main(){
  int n, m, p;
  cin >> n >> m >> p;
  vector<int> a(n);
  for(int i = 0; i < n; i++) cin >> a[i];
  vector<int> r;
  bool flag = true, flag2 = true;
  for(int i = 0; i < n; i++) {
    if(a[i] % p != 0) flag = false;
    if(a[i] % p == 0) r.push_back(a[i]);
    if(a[i] != 1) flag2 = false;
  }
  long long t = *max_element(r.begin(), r.end());
  if(t > m){
    cout << 1 << endl;
    return 0;
  }
  if(flag || flag2){
    cout << -1 << endl;
    return 0;
  }
  vector<int> b;
  for(int i = 0; i < n; i++){
    if(a[i] % p != 0) b.push_back(a[i]);
  }
  long long s = *max_element(b.begin(), b.end());
  int ans = 0;
  long long q = 1;
  while(q <= m){
    q *= s;
    ans++;
  }
  cout << ans << endl;
  return 0;
}