#include <iostream>
#include <cstdio>
#include <algorithm>

using namespace std;

int main() {
	int n, m, x, y;

	cin >> n >> m >> x >> y;
	x--;
	y--;
	x %= 2 * m;
	y %= 2 * m;

	if (x > y) {
		swap(x, y);
	}

	cout << (x == y || x + y == 2*m - 1 ? "YES" : "NO") << endl;
	return 0;
}