#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;
#define all(s) (s).begin(),(s).end()
#define vcin(n) for(ll i=0;i<ll(n.size());i++) cin>>n[i]
#define rever(vec) reverse(vec.begin(), vec.end())
#define sor(vec) sort(vec.begin(), vec.end())
#define fi first
#define se second
//const ll mod = 998244353;
const ll mod = 1000000007;
const ll inf = 2000000000000000000ll;
static const long double pi = 3.141592653589793;
template<class T,class U> void chmax(T& t,const U& u){if(t<u) t=u;}
template<class T,class U> void chmin(T& t,const U& u){if(t>u) t=u;}
ll modPow(ll a, ll n, ll mod) { ll ret = 1; ll p = a % mod; while (n) { if (n & 1) ret = ret * p % mod; p = p * p % mod; n >>= 1; } return ret; }
int main() {
  /* mod は 1e9+7 */
  ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
  cout<< fixed << setprecision(10);
  ll a,b,c;
  cin>>a>>b>>c;
  vector<ll> n(a);
  vcin(n);
  bool tmp=true;
  for(int i=0;i<a;i++){
    while(n[i]%c==0){
      n[i]/=c;
    }
    if(n[i]!=1){
      tmp=false;
    }
  }
  if(tmp){
    cout<<-1<<endl;
    return 0;
  }
  ll z=1;
  sor(n);
  rever(n);
  ll ans=0;
  while(z<b){
    z*=n[0];
    ans++;
  }
  cout<<ans<<endl;
}