#include <stdio.h>

int main(){
	int a,b,c,d;
	int taka,ao,num;
	
	scanf("%d%d%d%d",&a,&b,&c,&d);
	num = a/d;
	taka = a - num * d;
	ao = c - num*b;
	if(taka == 0){
		puts("No");
	}else if(ao - b <= 0){
		puts("Yes");
	}
	return 0;
}