#include <stdio.h>

int main(void){
	long long int h,w,n,k;
	long long int ans;
	scanf("%lld %lld %lld %lld", &h, &w, &n, &k);
	
	ans = (((h*w)%n+(n-1))%n)+1;
	if(ans == k){
		printf("YES\n");
	}else{
		printf("NO\n");
	}
	
	return 0;
}