#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define ALL(v) v.begin(), v.end()
typedef long long ll;

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

ll p;

ll f(ll x){
  while(x%p==0) x/=p;
  return x;
}

int main(){
  ll n,m;
  cin>>n>>m>>p;
  
  vector<ll> A(n);
  rep(i,n) cin>>A[i];
  
  ll ma=0;
  rep(i,n) ma=max(ma,A[i]);
  
  if(ma>m){
    cout<<1<<endl;
    return 0;
  }
  
  ll g=(m+ma-1)/ma;
  
  vector<ll> B(n);
  rep(i,n) B[i]=f(A[i]);
  
  ll ma1=0;
  rep(i,n) ma1=max(ma1,B[i]);
  
  if(ma1<2){
    cout<<-1<<endl;
    return 0;
  }
  
  ll now=1;
  int cnt=0;
  while(now<=g){
    now*=ma1;
    cnt++;
  }
  cout<<cnt+1<<endl;

  return 0;
}