#include <stdio.h>
int main(){
int a,b,c,d,e;
scanf("%d %d %d %d",&a,&b,&c,&d);
e = a/d;

for(int i = 0;i < e;i++){
	c -= b;
	if(c <= 0)
		printf("Yes");
		break;
	a -= d;
	if(a <= 0) 
		printf("No");
		break;}

}