#include <stdio.h>

int main(){
  int a,b,c,d;
  scanf("%d",&a);
  scanf("%d",&b);
  scanf("%d",&c);
  scanf("%d",&d);
  
  if((a+d-1)/d>(b+c-1)/c){
    printf("Yes");
  }else{
    printf("No");
  }
  return(0);
}