#include <stdio.h>

int main(void)
{
  int h1,h2,a1,a2;
  int flag=0;
  scanf("%d",&h1);
  scanf("%d",&a1);
  scanf("%d",&h2);
  scanf("%d",&a2);
  
  do
  {
    h2-=a1;
    
    if(h2<=0)
    {  
      flag=1;
      break;
    }
    h1-=a2;
  }while(h1>0);
  
  
  if(flag)
    printf("Yes");
  else 
    printf("No");
  
  return 0;
}
    