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