#include<stdio.h>
 
int main(){
  int a,b,c,d;
  int x,y;
  scanf("%d",&a);
  scanf("%d",&b); 
  scanf("%d",&c); 
  scanf("%d",&d);
 
  x=a/d;
  y=c/b;

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