#include<iostream>
#include<cstdio>
#include<cstring>
#include <cstdlib>  
#include <cmath>   
#include<cctype>
#include<string>
#include<set>
#include<iomanip>
#include <map>
#include<algorithm>
#include <functional>
#include<vector>
#include<climits>
#include<stack>
#include<queue>
#include <deque>
#include <climits>
#include <typeinfo>
#include <utility> 
#define all(x) (x).begin(),(x).end()
#define rep(i,m,n) for(int i = m;i < n;++i)
#define pb push_back
#define fore(i,a) for(auto &i:a)
#define rrep(i,m,n) for(int i = m;i >= n;--i)
#define INF INT_MAX/2
using namespace std;
using ll = long long;
using R = double;
using Data = pair<ll, vector<int>>;
const ll MOD = 1e9 + 7;
const ll inf = 1LL << 50;
struct edge { ll from; ll to; ll cost; };

int main() {
	int n, m, x, y;
	cin >> n >> m >> x >> y;
	
	x--, y--;

	int hanako;
	int temph = x % (2 * m);
	if (temph <= m - 1) {
		hanako = temph + 1;
	}
	else {
		hanako = 2 * m - temph;
	}
	int taro;
	int tempt = y % (2 * m);
	if (tempt <= m - 1) {
		taro = tempt + 1;
	}
	else {
		taro = 2 * m - tempt;
	}


	if (hanako == taro) {
		cout << "YES" << endl;
	}
	else {
		cout << "NO" << endl;
	}
	return 0;
}