#include <bits/stdc++.h>
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,b) FOR(i,0,b)
#define ALL(c) c.begin(),c.end()
#define PB push_back
#define TT second.second
#define SS second.first
#define FF first
using namespace std;
typedef long double ld;
typedef long long LL;
typedef double ut;
typedef vector<ut> VI;
typedef pair<ut,ut> pr;
typedef pair<ut,pr> ppr;
typedef vector<pr> Vpr;
typedef priority_queue<pr,Vpr,greater<pr> > PQ;
const int INF=1<<30;
const int BITSIZE=1<<12;
const int SIZE=10+2*1e4;

int main(){
	LL N,M,X,Y;
	cin >> N >> M >> X >> Y;
	M*=2;
	if(X%M==Y%M || (X%M+Y%M)==M+1)
		cout << "YES" << endl;
	else
		cout << "NO" << endl;
	return 0;
}