/**
 *   @FileName	a.cpp
 *   @Author	kanpurin
 *   @Created	2021.01.08 21:45:08
**/

#include "bits/stdc++.h" 
using namespace std; 
typedef long long ll;

int main() {
    int n,m,p;cin >> n >> m >> p;
    vector<int> a(n);
    for (int i = 0; i < n; i++) {
        cin >> a[i];
        if (p == 1) continue;
        while (a[i] % p == 0) {
            a[i] /= p;
        }
    }
    sort(a.rbegin(), a.rend());
    int ans = 0;
    ll x = 1;
    if (x >= m) {
        cout << 0 << endl;
        return 0;
    }
    if (p == 1 || a[0] == 1) {
        cout << -1 << endl;
        return 0;
    }
    while(x < m) {
        x *= a[0];
        ans++;
    }
    cout << ans << endl;
    return 0;
}