int main(void)
{
  int a,b,c,d;
  int flag = 0;
  
  scanf("%d%d%d%d",&a,b,c,d);
  
  
  while(flag == 0){
    
    a -= d;
    if(a < 1)
      flag = 2;
    
     c -= b;
    if(c < 1)
      flag = 1;
  }
  
  if(flag == 1)
  printf("Yes");
  
  else 
    printf("No");
  
  return 0;
}