#include <stdio.h>

int main(){
	int tt, tk, at, ak;
	
	scanf("%d %d %d %d", &tt, &tk, &at, &ak);
	
	while(1){
		at=at-tk;
		if(at<=0);{
			break;
		}
		tt=tt-ak;
		if(tt<=0){
			break;
		}
	}
	if(at<=0){
		printf("Yes");
	}else{
		printf("No");
	}
	
	return 0;
}