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