#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define chmin(x,y) x = min((x),(y));
#define chmax(x,y) x = max((x),(y));
using namespace std;
using ll = long long ;
using P = pair<int,int> ;
using pll = pair<long long,long long>;
const int INF = 1e9;
const long long LINF = 1e17;
const int MOD = 1000000007;
//const int MOD = 998244353;
const double PI = 3.14159265358979323846;

int main(){
    ll n,m,p;
    cin >> n >> m >> p;
    vector<ll> a(n);
    vector<int> cnt(n,1);
    ll mx = 0;
    int mx_idx = -1;
    bool ok = false;
    rep(i,n){
        cin >> a[i];
        if(mx < a[i]){
            mx = a[i];
            mx_idx = i;
        }
        while(a[i]%p==0){
            a[i] /= p;
            ++cnt[i];
        }
        if(a[i]!=1) ok = true;
    }
    if(!ok && mx < m){
        cout << -1 << endl;
        return 0;
    }
    double mxx = 0;
    int idx = -1;
    rep(i,n){
        if(mxx*cnt[i] < a[i]){
            mxx = a[i]/(double)cnt[i];
            idx = i;
        }
    }
    ll ans = 0;
    ll x = 1;
    //cout << idx << endl;
    //cout << cnt[idx] << endl;
    while(x < m){
        x *= a[idx];
        ans += cnt[idx];
    }
    ans -= cnt[idx]-1;
    ll res = 1;
    x = mx;
    while(x < m){
        x *= a[idx];
        res += cnt[idx];
    }
    ans = min(ans,res);
    cout << ans << endl;
    return 0;
}