import java.util.*;

public class Main {
 	public static void main (String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		double x = sc.nextInt();
		double y = sc.nextInt();
		int n = sc.nextInt();
		int prev = 0;
		for (int i = 0; i < n; i++) {
		    int now = sc.nextInt();
		    if (now / y < prev / x) {
		        System.out.println("NO");
		        return;
		    }
		    prev = now;
		}
		System.out.println("YES");
	}
}