#include<cstdio>
#include<iostream>
#include<algorithm>
#include<string>
#include<queue>
#include<vector>
#include<functional>
#include<cmath>
#include<map>
#include<stack>
#include<set>
#include<numeric>

using namespace std;
typedef long long ll;
typedef pair<int, int> pi;
typedef pair<ll, ll> pl;

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

	ll hanako, tarou;
	if ((X / M) % 2 == 0) {
		hanako = X % M;
		if (X%M == 0)hanako = 1;
	}
	else {
		int a = X % M;
		if (X % M == 0)a = 1;
		hanako = (M - a) + 1;
	}

	if ((Y / M) % 2 == 0) {
		tarou = Y % M;
		if (Y%M == 0)tarou = 1;
	}
	else {
		int a = Y%M;
		if (Y%M == 0)a = 1;
		tarou = (M- a) + 1;
	}
	
	if (hanako == tarou)cout << "YES" << endl;
	else cout << "NO" << endl;

	return	0;
}