#include<stdio.h>

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