#include <iostream>
#include <vector>
#include <iomanip>
#include <algorithm>
#include <cmath>
using namespace std;
using ll = long long;

ll n, m, x, y;

int main()
{
  cin >> n >> m >> x >> y;
  --x, --y;
  ll xshou = x / m, xamari = x % m, yshou = y / m, yamari = y % m;
  ll xclass = (xshou & 1 ? m - xamari - 1 : xamari);
  ll yclass = (yshou & 1 ? m - yamari - 1 : yamari);
  cout << (xclass == yclass ? "YES" : "NO") << endl;

  return 0;
}