#include <stdio.h>

int main(void){
	int a, b, c, d;
	int count=0;
	
	scanf("%d %d %d %d",&a,&b,&c,&d);
	
	while(a > 0 && c > 0){
		if(count==0)
			c -= b;
		else
			a -= d;
		count = !count;
	}
	
	if(a <= 0)
		printf("Yes");
	else
		printf("No");
	return 0;	
}