#include <bits/stdc++.h>
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 >= M) X = M * 2 - X - 1;
	if (Y >= M) Y = M * 2 - Y - 1;

	puts(X == Y ? "YES" : "NO");
}