import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.PriorityQueue;
import java.util.Scanner;

public class Main {
	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		final int X = sc.nextInt();
		final int Y = sc.nextInt();
		final int N = sc.nextInt();
		
		int[] array = new int[N];
		for(int i = 0; i < N; i++){
			array[i] = sc.nextInt();
		}
		
		for(int i = 0; i < N - 1; i++){
			if(array[i] * Y > array[i + 1] * X){
				System.out.println("NO");
				return;
			}
		}
		
		System.out.println("YES");
	}
}