#include <stdio.h>
int main(void){
	int a, b, c, d;
	while(1){
		scanf("%d %d %d %d", &a, &b, &c, &d);
		if((1<=a)&&(a<=100)&&(1<=b)&&(b<=100)){
			if((1<=c)&&(c<=100)&&(1<=d)&&(d<=100)){
				break;
			}
		}
	}
	 while(1){
		 c = c - b;
		 if(c<=0){
			 printf("Yes");
			 break;
		 }
		 a = a - d;
		 if(a<=0){
			 printf("No");
			 break;
		 }
	 }
	return 0;
}
