#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(n);++i)
#define all(a) (a).begin(),(a).end()
#define dunk(a) cout << (a) << endl
using namespace std;
typedef long long ll;

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	ll n, m, x, y;
	cin >> n >> m >> x >> y;
	
	puts((x - y) % (2 * m) == 0 || (x + y) % (2 * m) == 1 ? "YES" : "NO");

	return 0;
}