#define _CRT_SECURE_NO_WARNINGS
#include <bits/stdc++.h>
using namespace std;
#define len(n) (int)n.length()
#define pb push_back
#define ll long long
#define make_pair mkp
#define REP(i, n) for(int i = 0;i < n;i++)
#define REPR(i, n) for(int i = n;i >= 0;i--)
#define FOR(i, m, n) for(int i = m;i < n;i++)
#define ALL(v) (v).begin(), (v).end()
#ifdef DBGPRT
#define dbg(n) cerr << "//" << #n << ":" << n <<endl
#else
#define dbg(n) ;
#endif
typedef pair<ll, ll> LLARR;
#define INF 999999999
const double PI = 3.1415926535897932384626433832795;

int main()
{
	ios::sync_with_stdio(false);

	int n, m, x, y;
	cin >> n >> m >> x >> y;

	int xj = -1;
	if (((x-1)/m) %2 == 0)
	{
		xj = x - (((x-1)/m)*m);
	}
	else
	{
		xj = ((((x-1)/m)+1) * m) - x + 1;
	}
	
	dbg(xj);
	int yj = -1;
	if (((y-1)/m) %2 == 0)
	{
		yj = y - (((y-1)/m)*m);
	}
	else
	{
		yj = ((((y-1)/m)+1) * m) - y + 1;
	}
	
	dbg(yj);
	cout << ((xj == yj) ? "YES" : "NO") << endl;
	return 0;
}