#define _CRT_SECURE_NO_WARNINGS
#include <cstdio>
#include <iostream>
#include <string>
#include <algorithm>
typedef unsigned long long ull;
using namespace std;
int N, M;
int solve (int X){
	int k = X % (2 * M);
	if (k < M)return k + 1;
	else return (2 * M) - k;
}
int main() {
	int X, Y;
	cin >> N >> M >> X >> Y;
	if (solve(X-1) == solve(Y-1)) {
		cout << "YES" << endl;
	}
	else {
		cout << "NO" << endl;
	}
}