#include<stdio.h>
int main()
{
	int a,b,c,d;
	int cnt1,cnt2;
	scanf("%d %d %d %d",&a,&b,&c,&d);
	cnt1=0;
	cnt2=0;
	while(1){
		if(a<=0) break;
		else{
			c=c-b;
			cnt1++;
		}
		if(c<=0) break;
		else{
			a=a-d;
			cnt2++;
		}
	}
	if(cnt1>cnt2) printf("Yes\n");
	else printf("No\n");
	return 0;
}
