import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Main {
	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String[] sa = br.readLine().split(" ");
		int n = Integer.parseInt(sa[0]);
		int m = Integer.parseInt(sa[1]);
		int p = Integer.parseInt(sa[2]);
		sa = br.readLine().split(" ");
		int[] a = new int[n];
		for (int i = 0; i < n; i++) {
			a[i] = Integer.parseInt(sa[i]);
		}
		br.close();

		int[] b = new int[n];
		int[] c = new int[n];
		for (int i = 0; i < n; i++) {
			if (a[i] > m) {
				System.out.println(1);
				return;
			}
			b[i] = a[i];
			while (b[i] % p == 0) {
				b[i] /= p;
			}
			c[i] = m / a[i] + 1;
		}

		int ans = Integer.MAX_VALUE;
		for (int i = 0; i < n; i++) {
			if (b[i] == 1) {
				continue;
			}
			long x = 1;
			int cnt = 0;
			while (x < c[i]) {
				cnt++;
				x *= b[i];
			}
			ans = Math.min(ans, cnt + 1);
		}
		if (ans == Integer.MAX_VALUE) {
			ans = -1;
		}
		System.out.println(ans);
	}
}