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

int main(void) {
#ifdef DEBUG
  freopen("input.txt", "r", stdin);
#endif

  ios_base::sync_with_stdio(false);
  cin.tie(NULL);

  int N, M, X, Y;
  cin >> N >> M;
  cin >> X >> Y;

  int class_[2];
  int i = 0;
  for (int j : {X, Y}) {
    int d = (j - 1) / M;
    int m = (j - 1) % M;
    if (d % 2) {
      class_[i] = M - m;
    } else {
      class_[i] = m + 1;
    }
    i++;
  }
  if (class_[0] == class_[1])
    cout << "YES" << endl;
  else
    cout << "NO" << endl;

  return 0;
}