#include<stdio.h>

int main(void)
{

		int a, b,c,d;

		scanf("%d %d %d %d", &a, &b,&c,&d);
		while (1)
		{
			c -= b;
			if (c<=0) {
				printf("Yes");
				return 0;
			}
			a -= d;
			if (a <= 0) {
				printf("No");
				return 0;
			}
		}
	
}