#include <iostream>
#include <vector>
#include <cstring>
#include <string>
#include <algorithm>
#include <iomanip>
using namespace std;
typedef long long ll;
int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

	ll N, M, X, Y;
	cin >> N >> M >> X >> Y;
	X--, Y--;

	int r1 = X / M, r2 = Y / M;
	if(r1 % 2 == r2 % 2) {
		if(X % M == Y % M) {
			cout << "YES" << endl;
		}
		else {
			cout << "NO" << endl;
		}
	}
	else {
		if(X % M == M - 1 - Y % M) {
			cout << "YES" << endl;
		}
		else {
			cout << "NO" << endl;
		}
	}
}