#include <stdio.h>
int main (){
int a,b,c,d,t,y;

scanf("%d",&a);
scanf("%d",&b);
scanf("%d",&c);
scanf("%d",&d);
t=a;
y=c;
while(1)
{
  if(t>0 && y>0)
  {
   y=y-b;
    if(y<=0) 
    {
      printf("Yes");
      break;
    }
      
  t=t-d;
    if(t<=0)
    {
      printf("No");
      break;
    }
  }


}
}
