#include<stdio.h>

int main(int argc, char const *argv[]){
	long x,y,n,a[80],i;
	scanf("%ld %ld",&x,&y);
	scanf("%ld",&n);
	for(i=0;i<n;i++){
		scanf("%ld",&a[i]);
		if(i>0){
			if(a[i-1]*y/x>a[i]){
				printf("NO\n");
				return 0;
			}
		}
	}
	printf("YES\n");
	return 0;
}