#include <bits/stdc++.h>
using namespace std;
int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);  
	int n, m;
	cin >> n >> m;
	int x[2];
	cin >> x[0] >> x[1];
	for(int i = 0; i < 2; i++) {
		x[i]--;
		x[i] %= (2 * m);
		x[i] = min(x[i], 2 * m - 1 - x[i]);
	}
	cout << (x[0] == x[1] ? "YES" : "NO") << endl;
	return 0;
}