import java.util.*;

public class Main {
	static Scanner sc = new Scanner(System.in);
	public static void main(String[] args) {
		int student = sc.nextInt();
		int teacher = sc.nextInt();
		int n = sc.nextInt();
		int[] intersection = new int[n];
		for (int i=0; i<n; i++) {
			intersection[i] = sc.nextInt();
		}
		
		boolean F = true;
		for (int i=0; i<n-1; i++) {
			if (intersection[i]*teacher > intersection[i+1]*student) {F = false;}
		}
		System.out.println(F==true?"YES":"NO");
	}
}