import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int x = scan.nextInt();
        int y = scan.nextInt();
        int n = scan.nextInt() ;
        int[] list = new int[n];
        boolean flg = true;
        for(int i = 0 ; i < n ; i++ ){
        	list[i] = scan.nextInt();
        	if(flg && i > 0 && list[i-1]*y > list[i]*x){
        		flg = false;
        	}
        }
        if(flg){
        	System.out.println("YES");
        }else{
        	System.out.println("NO");
        }
    }
}