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


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