#include <bits/stdc++.h>
using namespace std;

const string msg[] = { "NO", "YES" };

signed main(){
  int N, M; cin >> N >> M;
  int X, Y; cin >> X >> Y; --X, --Y;
  if( X / M % 2 == Y / M % 2 )
    cout << msg[ X % M == Y % M ] << endl;
  else
    cout << msg[ X % M == M - 1 - Y % M ] << endl;
  return 0;
}