#include<bits/stdc++.h>
// #include<atcoder/all>

using namespace std;
// using namespace atcoder;
using ll = long long;
using ull = unsigned long long;
using P = pair<int,int>;
#define rep(i,n) for(ll i = 0;i < (ll)n;i++)
#define ALL(x) (x).begin(),(x).end()
#define MOD 1000000007

int main(){
  
  ll n,m,p;
  cin >> n >> m >> p;
  ll k = 0;
  ll mx = 0;
  rep(i,n){
    ll x;cin >> x;
    mx = max(mx,x);
    while(x%p == 0)x /= p;
    k = max(k,x);
  }
  if(mx > m)cout << 1 << "\n";
  else if(k == 1)cout << -1 << "\n";
  else {
    int res = 1;
    ll g = mx;
    while(g <= m)g *= k,res++;
    cout << res << "\n";
  }


  return 0;
}