#include <bits/stdc++.h>

//const static double	de_PI	= 3.14159265358979323846;
//const static int	de_MOD	= 1000000007;
//const static int	de_MAX	= 999999999;
//const static int	de_MIN = -999999999;

int main(void) {

	//std::ifstream inf("123.txt");	std::cin.rdbuf(inf.rdbuf());
	int N = 0, M = 0, X = 0, Y = 0;
	std::cin >> N >> M >> X >> Y;

	int Xr = 0, Xc = 0, Yr = 0, Yc = 0;

	Xr = (X - 1) / M;
	if (Xr % 2 == 0) { Xc = (X - 1) % M; }
	else { Xc = M - 1 - (X - 1) % M; }

	Yr = (Y - 1) / M;
	if (Yr % 2 == 0) { Yc = (Y - 1) % M; }
	else { Yc = M - 1 - (Y - 1) % M; }

	if (Xc == Yc) { std::cout << "YES" << std::endl; }
	else { std::cout << "NO" << std::endl; }

}