#include <iostream>
#include <cmath>
using namespace std;

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

	long long int a, b;
	a = ceil((double)x / m);
	b = ceil((double)y / m);

	x -= m*(a-1);
	y -= m*(b-1);
	if (!(a % 2)) x = m - x + 1;
	if (!(b % 2)) y = m - y + 1;

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

	return 0;
}