#include "bits/stdc++.h"

using namespace std;

void solve(void)
{
	int n, m, x, y;
	cin >> n >> m >> x >> y;
	x--, y--;
	x %= 2 * m;
	y %= 2 * m;
	if (x == y || x+y == 2*m-1)
	{
		cout << "YES" << endl;
	}
	else
	{
		cout << "NO" << endl;
	}
}

int main()
{
	solve();
	//cout << "yui(*-v・)yui" << endl;
	return 0;
}