#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<ll> VL;
typedef vector<VL> VVL;
typedef pair<int, int> PII;

#define FOR(i, a, n) for (ll i = (ll)a; i < (ll)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()
#define MOD 1000000007
#define INF (1LL<<25)     //33554432
#define PI 3.14159265359
#define EPS 1e-12
//#define int ll

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

  x = (x-1)%(2*m);
  y = (y-1)%(2*m);
  if(x >= m) {
    x -= (2*m-1);
    x *= -1;
  }
  if(y >= m) {
    y -= (2*m-1);
    y *= -1;
  }

  if(x == y) {
    cout << "YES" << endl;
  } else {
    cout << "NO" << endl;
  }

  return 0;
}