#include<stdio.h>
int main(void){
	int a, b, c, d;
	scanf("%d", &a);
	scanf("%d", &b);
	scanf("%d", &c);
	scanf("%d", &d);
	if((c+b-1)/b <= (a+d-1)/d){
		printf("Yes\n");
	}
	else{
		printf("No\n");
	}
	return 0;
}