#include <stdio.h> 


int main(){
	int TakahashiBlood,TakahashiAttack,AokiBlood,AokiAttack;
	scanf("%d",&TakahashiBlood);
	scanf("%d",&TakahashiAttack);
	scanf("%d",&AokiBlood);
	scanf("%d",&AokiAttack);
	while((TakahashiBlood>0)&&(AokiBlood)){
		AokiBlood=AokiBlood-TakahashiAttack;
		if (AokiBlood>0)
			TakahashiBlood=TakahashiBlood-AokiAttack;
	}
	if(TakahashiBlood>0)
		printf("Yes");
	else
		printf("No");
		
}