#include <bits/stdc++.h>
using namespace std;
 
#define fi first
#define se second
#define pb push_back
using vi = vector <int>;
using ll = long long;
using vl = vector <ll>;
using pii = pair <int, int>;
//~ const ll mod = 998244353;
const ll mod = 1e9 + 7;
ll qpow(ll a, ll b, ll m = mod) { ll r = 1, t = a;
	for(; b; b /= 2) { if(b & 1) r = r * t % m; t = t * t % m; } return r; }

const int N = 2e5 + 11;

int a[N], b[N];

int main() {
	ios :: sync_with_stdio(false);
	
	int n, m, p; cin >> n >> m >> p;
	for(int i = 0; i < n; i ++) {
		cin >> a[i];
		b[i] = a[i];
		while(a[i] % p == 0)
			a[i] /= p;
	}
	
	int x = *max_element(a, a + n);
	int y = *max_element(b, b + n); // last only
	
	if(m == 1)
		cout << "0\n";
	else if(x == 1) {
		if(y > m)
			cout << "1\n";
		else
			cout << "-1\n";
	} else {
		ll t = 1, c = 0;
		while(t <= m) {
			if(t * y > m) {
				c ++;
				break;
			} else {
				t *= x;
				c ++;
			}
		}
		cout << c << '\n';
	}
}