#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <cstring>
#include <queue>
#include <stack>
#include <math.h>
#include <iterator>
#include <vector>
#include <string>
#include <set>
#include <math.h>
#include <iostream> 
#include<map>
#include <stdlib.h>
#include <list>
#include <typeinfo>
#include <list>
#include <set>
#include <iomanip>
using namespace std;
#define MAX_MOD 1000000007
#define REP(i,n) for(int i = 0;i < n;++i)
int main() {
	int n, m, x, y;
	cin >> n >> m >> x >> y;
	m *= 2;
	int taro_class = x%m;
	int hanako_class = y%m;
	if (taro_class > m/2) {
		taro_class = m + 1 - taro_class;
	}
	if (hanako_class > m / 2) {
		hanako_class = m + 1 - hanako_class;
	}
	if (hanako_class == 0) hanako_class = 1;
	if (taro_class == 0) taro_class = 1;
	if (taro_class == hanako_class) {
		cout << "YES" << endl;
	}
	else {
		cout << "NO" << endl;
	}
}