#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <queue>
#include <climits>
using namespace std;

typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int,int> pii;

#define INF INT_MAX/3
#define REP(i,n) for(int i=0;i<n;i++)


int N,M,X,Y;


int main(){
	cin>>N>>M;
	cin>>X>>Y;
	bool kekka = false;
	if(M == 1)kekka = true;
	int p = X % (2*M);
	int q = Y % (2*M);
	if(p <= M && (q > M || q == 0)){
		int k = 2*M - p + 1;
		if(k%(2*M) == q)kekka = true;
	}
	else if((p > M || p==0) && q <= M){
		int k = 2 * M - q + 1;
		if(k%(2*M) == p)kekka = true;
	}
	else{
		if(p == q){
			kekka = true;
		}
	}
	
	if(kekka){
		cout<<"YES"<<endl;
	}else{
		cout<<"NO"<<endl;
	}

	return 0;
	
}