#include <stdio.h>
#include <stdlib.h>

int main(void){
	int a,b,c,d;
	
	scanf("%d %d %d %d",&a,&b,&c,&d);
	
	while(1){
		c-=b;
		if(c<=0){
			printf("Yes\n"); break;
		}
		a-=d;
		if(a<=0){
			printf("No\n"); break;
		}
	}
	return 0;
}