/*** author: yuji9511 ***/
#include <bits/stdc++.h>
// #include <atcoder/all>
// using namespace atcoder;
using namespace std;
using ll = long long;
using lpair = pair<ll, ll>;
using vll = vector<ll>;
const ll MOD = 1e9+7;
const ll INF = 1e18;
#define rep(i,m,n) for(ll i=(m);i<(n);i++)
#define rrep(i,m,n) for(ll i=(m);i>=(n);i--)
ostream& operator<<(ostream& os, lpair& h){ os << "(" << h.first << ", " << h.second << ")"; return os;}
#define printa(x,n) for(ll i=0;i<n;i++){cout<<(x[i])<<" \n"[i==n-1];};
void print() {}
template <class H,class... T>
void print(H&& h, T&&... t){cout<<h<<" \n"[sizeof...(t)==0];print(forward<T>(t)...);}

void solve(){
    ll n,m,p;
    cin >> n >> m >> p;
    vll a(n);
    rep(i,0,n) cin >> a[i];
    vll cnt_p(n, 0);
    vll b(n);
    rep(i,0,n){
        ll v = a[i];
        while(v % p == 0){
            v /= p;
            cnt_p[i]++;
        }
        b[i] = v;
    }
    rep(i,0,n){
        if(a[i] > m){
            print(1);
            return;
        }
    }
    bool ok = false;
    rep(i,0,n){
        if(b[i] != 1) ok = true;
    }

    if(not ok){
        print(-1);
        return;
    }
    ll max_val = 0;
    rep(i,0,n){
        max_val = max(max_val,a[i]);
    }

    ll ans = INF;
    rep(i,0,n){
        if(b[i] == 1) continue;
        ll res = 0, cur = 1;
        while(true){
            if(cur * max_val > m){
                res++;
                break;
            }else{
                cur *= b[i];
                res += 1 + cnt_p[i];
            }
        }
        ans = min(ans, res);

    }
    print(ans);




}

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    solve();
}