#include <iostream>

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

	std::cin >> n >> m >> x >> y;

	x--;
	y--;

	x %= m * 2;
	y %= m * 2;

	//std::cout << x << " " << y << std::endl;

	if (x == y || x + y == m * 2 - 1) {
		std::cout << "YES" << std::endl;
	} else {
		std::cout << "NO" << std::endl;
	}

	return 0;
}