#include <stdio.h>

int main(void){
	
	int a,b,c,d;
	scanf("%d %d %d %d",&a,&b,&c,&d);
	
	int ra = a/d;
	if( a%d != 0 ) ra++;
	int rc = c/b;
	if( c%b != 0 ) rc++;
	if( rc > ra ) printf("No");
	else printf("Yes");
	
}