#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)!=0){
    a/d=(a/d)+1;
  }  
  if((c%b)!=0){
    c/b=(c/b)+1;
  }
  if((a/d)<(c/b)){
    printf("No\n");
  }else{
    printf("Yes\n");
  }
  return 0;
}