#include <bits/stdc++.h>
using namespace std;

using ll = long long;
using pii = pair<int, int>;
#define REP(i, x) for(int i = 0; i < (x); i++)

ll res, x = 1;

int main() {
	int n, m, p;
	cin >> n >> m >> p;
	vector a(n, 0);
	REP(i, n) { cin >> a[i]; }

	int amax = *max_element(a.begin(), a.end());

	vector<pii> b(n);
	REP(i, n) {
		int num = 1;
		while(a[i] % p == 0) a[i] /= p, num++;
		b[i] = pii(a[i], num);
	}

	auto f = [](pii a, pii b) {
		return a.first / (double)a.second < b.first / (double)b.second;
	};

	sort(b.rbegin(), b.rend(), f);

	if(amax <= m and b[0].first == 1) {
		puts("-1");
		return 0;
	}

	int lim = m / amax + 1;

	while(x < lim) x *= b[0].first, res += b[0].second;
	
	printf("%d\n", res + 1);
}