#include<stdio.h>
int main()
{
	int a,b,c,d;
	scanf("%d %d %d %d",&a,&b,&c,&d);

    for(;;){
		c-=b;
		if(c <= 0){
			printf("Yes\n");
			break;
        }
		a-=d;
		if(a <= 0){
			printf("No\n");
			break;
        }
	}
	return 0;
}
