#include <stdio.h>
#include <stdlib.h>

int main(){
	unsigned X, Y, N, *A;
	scanf("%d%d%d", &X, &Y, &N);
	A = (unsigned *)malloc(sizeof(unsigned) * N);
	for(unsigned i = 0; i < N; i++) scanf("%d", A + i);

	for(unsigned i = 0; i < N - 1; i++) if(A[i + 1] < A[i] * Y / X){
		printf("NO");
		return 0;
	}
	printf("YES");
	return 0;
}