#include "bits/stdc++.h"
#define _CRT_SECURE_NO_WARNINGS
#define rep(i,n) for(int i = 0;i < n;i++)
#define REP(i,n,k) for(int i = n;i < k;i++)
#define P(p) cout << (p) << endl;
#define sP(p) cout << setprecision(15) << fixed << p << endl;
#define Pi pair<int,int>
#define IINF 1e9
#define LINF 1e18
#define vi vector<int>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
int dx[] = { 1, 0,-1,0 };
int dy[] = { 0, 1,0,-1 };

bool isPrime(int n) {
	if (n <= 1)return false;
	if (n == 2)return true;
	if (n % 2 == 0)return false;
	for (int i = 3; i*i <= n; i += 2) {
		if (n%i == 0)return false;
	}
	return true;
}

void bubbleSort(vector<int> v) {
	vector<pair<int, int> > ans;
	for (int i = 0; i < v.size() - 1; i++) {
		for (int j = v.size()-1; j > i; j--) {
			if (v[j]>v[j - 1]) {
				int t = v[j];
				v[j] = v[j - 1];
				v[j - 1] = t;
				ans.push_back(make_pair(j-1,j));
			}
		}
	}
	P(ans.size());
	rep(i, ans.size()) {
		cout << ans[i].first << " " << ans[i].second << endl;
	}
}

void solve() {
	int n, m, x, y;
	cin >> n >> m >> x >> y;
	x = x - (x / (m*2))*(m*2);
	y = y - (y / (m*2))*(m*2);
	if (x == 0)x = 1;
	if (y == 0)y = 1;
	if (x > m) {
		x = x - (x / m)*m;
		x = m - (x-1);
	}
	if (y > m) {
		y = y - (y / m)*m;
		y = m - (y-1);
	}
	if (x == y) {
		P("YES");
	}
	else {
		P("NO");
	}
}

int main() {
	solve();
	return 0;
}