#include<stdio.h>
int main(void){
	int x,y,n,a[128],i;
	scanf("%d%d%d",&x,&y,&n);
	for(i = 1;i <= n;i++){scanf("%d",&a[i]);}
	for(i=1;i<=n-1;i++){
		if(y*a[i]>x*a[i+1]){printf("NO\n");return 0;}
	}
	printf("YES\n");
	return 0;
}