#include<stdio.h>
#include<math.h>
#include<stdlib.h>

int main(void){
	int a,b,c,d;
	double r,l;

	scanf("%d %d %d %d",&a,&b,&c,&d);

	do{
		if( c - b <=0){
			printf("Yes\n");
			break;
		}
		c -= b;
		if( a - d <=0){
			printf("No\n");
			break;
		}
		a -= d;
	}while(1);

	return 0;
}