import 'dart:io';
 
void main(List<String> args){
  List<int> N = stdin.readLineSync().split(' ').map((i) => int.parse(i)).toList();
  int takahashi = N[2]/N[1];
  int aoki = N[0]/N[3];
  if(N[2]%N[1]!=0) takahashi = takahashi + 1;
  if(N[0]%N[3]!=0) aoki = aoki + 1;
  if(takahashi > aoki) print("No");
  else print"Yes");
}