/* -*- coding: utf-8 -*-
 *
 * 396.cc: No.396 クラス替え - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

/* typedef */

/* global variables */

/* subroutines */

inline int cnum(int a, int m) {
  return ((a / m) & 1) ? m - 1 - a % m : a % m;
}

/* main */

int main() {
  int n, m, x, y;
  cin >> n >> m >> x >> y;
  x--, y--;

  cout << (cnum(x, m) == cnum(y, m) ? "YES" : "NO") << endl;
  return 0;
}