#include<stdio.h>

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

  int f=0;

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

  while(1){
	c = c-b;
	if(c<=0){
	  f=1;
	  break;
	}

	a = a-d;
	if(a<=0){
	  break;
	}

  }

  if(f==0){
	printf("No\n");
  }else{
	printf("Yes\n");
  }

  return 0;
}
