#include<bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for(int i=a;i<b;i++)

int N, M, X, Y;
//-----------------------------------------------------------------
int main() {
	cin >> N >> M >> X >> Y;

	X--; Y--;

	//cout << X << "," << Y << endl;

	X = X % (2 * M);
	Y = Y % (2 * M);

	//cout << X << "," << Y << endl;

	if (M <= X) X = M - 1 - (X % M);
	if (M <= Y) Y = M - 1 - (Y % M);

	//cout << X << "," << Y << endl;

	if (X == Y)
		cout << "YES" << endl;
	else
		cout << "NO" << endl;
}