#include <stdio.h>

int main () {
	int healthTaka;
	int attackTaka;
	int healthAoki;
	int attackAoki;
	scanf("%d %d %d %d",&healthTaka,&attackTaka,&healthAoki,&attackAoki);
	while(1)
	{
		healthAoki = healthAoki - attackTaka;
		if(healthAoki < 1)
		{
			printf("Yes");
			break;
		}
		healthTaka = healthTaka - attackAoki;
		if(healthTaka < 1)
		{
			printf("No");
			break;
		}
	}
	return 0;
}
