#include<bits/stdc++.h>
using namespace std;
using Int = long long;
//INSERT ABOVE HERE
signed main(){
  Int n,m,x,y;
  cin>>n>>m>>x>>y;
  x--;y--;
  Int a=(x%(2*m));
  if(a>=m) a=(2*m-(a+1))%m;
  Int b=(y%(2*m));
  if(b>=m) b=(2*m-(b+1))%m;
  //cout<<a<<" "<<b<<endl;
  cout<<(a==b?"YES":"NO")<<endl;
  return 0;
}