#define _CRT_SECURE_NO_WARNINGS // #pragma warning(disable:4996)
#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <functional>
#include <sstream>
#include <cmath>
using namespace std; 

#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define pb push_back
#define mp(a,b) make_pair(a,b)
#define all(a) a.begin(),a.end()

typedef pair<int, int> Pii;
typedef vector<int> V;
typedef vector<V> VV;
typedef vector<VV> VVV;
typedef long long ll;
const int inf = 1e9;
const int mod = 1e9 + 7;

int N, M, X, Y;

int main()
{
	cin >> N >> M >> X >> Y;
	int a = (X-1) % M;
	int b = (Y-1) % M;
	int a2 = (X-1) / M;
	int b2 = (Y-1) / M;
	//printf("a=%d b=%d a2=%d b2=%d\n",a,b,a2,b2);
	
	if(a2%2==b2%2) {
		if(a==b) cout << "YES" << endl;
		else cout << "NO" << endl;
	} else {
		if(a2) {
			if((M-a-1)==b) cout << "YES" << endl;
			else cout << "NO" << endl;
		} else if (b2) {
			if((M-b-1)==a) cout << "YES" << endl;
			else cout << "NO" << endl;
		}
	}

	return 0;
}