#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)
#define FOR(i,b,e) for (int i=(int)(b); i<(int)(e); i++)
#define ALL(x) (x).begin(), (x).end()

const double PI = acos(-1);

int calc(int x, int n, int m) {
  x %= 2 * m;
  return x <= m ? x : 2 * m - x + 1;
}

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  int n, m, x, y;
  cin >> n >> m >> x >> y;

  if (calc(x, n, m) == calc(y, n, m))
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
  
  return 0;
}