#include <bits/stdc++.h>

using namespace std;

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()

template<typename A, typename B> inline bool chmax(A &a, B b) { if (a<b) { a=b; return 1; } return 0; }
template<typename A, typename B> inline bool chmin(A &a, B b) { if (a>b) { a=b; return 1; } return 0; }

typedef unsigned long long ull;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, pii> P;

const ll INF = 1ll<<29;
const ll MOD = 1000000007;
const double EPS  = 1e-10;

int main() {
	ll n, m, x, y;
	cin >> n >> m >> x >> y;
	
	x--; y--;
	
	int ca = x % (2*m);
	int cb = y % (2*m);
	
	if (ca >= m) ca = m - 1 - (ca - m);
	if (cb >= m) cb = m - 1 - (cb - m);
	
	puts(ca == cb ? "YES" : "NO");
	return 0;
}