#include <iostream>
#include <cstdio>
#include <cmath>
#include <ctime>
#include <cstdlib>
#include <cassert>
#include <vector>
#include <list>
#include <stack>
#include <queue>
#include <deque>
#include <map>
#include <set>
#include <bitset>
#include <string>
#include <algorithm>
#include <utility>
#include <complex>
#define rep(x, s, t) for(llint (x) = (s); (x) <= (t); (x)++)
#define chmin(x, y) (x) = min((x), (y))
#define chmax(x, y) (x) = max((x), (y))
#define all(x) (x).begin(),(x).end()
#define inf 1e18

using namespace std;

typedef long long llint;
typedef long long ll;
typedef pair<llint, llint> P;

ll n, m, p;
ll a[200005];

int main(void)
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	cin >> n >> m >> p;
	m++;
	rep(i, 1, n) cin >> a[i];
	sort(a+1, a+n+1);
	
	if(m == 1){
		cout << 0 << endl;
		return 0;
	}
	if(a[n] >= m){
		cout << 1 << endl;
		return 0;
	}
	m = (m+a[n]-1)/a[n];
	
	ll ans = inf;
	rep(i, 1, n){
		ll cnt = 0, cnt2 = 0, mul = a[i];
		for(; mul % p == 0; mul /= p) cnt++;
		if(mul == 1) continue;
		for(ll x = 1; x < m; x *= mul) cnt2++;
		chmin(ans, (cnt+1)*cnt2);
	}
	if(ans > inf/2) cout << -1 << endl;
	else cout << ans+1 << endl;
	
	return 0;
}