#include<iostream>
#include<vector>
#include<string>
#include<algorithm>	
#include<map>
#include<set>
#include<utility>
#include<cmath>
#include<cstring>
#include<queue>
#include<stack>
#include<cstdio>
#include<sstream>
#include<iomanip>
#include<assert.h>
#define loop(i,a,b) for(int i=a;i<b;i++) 
#define rep(i,a) loop(i,0,a)
#define pb push_back
#define mt make_tuple
#define all(in) in.begin(),in.end()
#define shosu(x) fixed<<setprecision(x)
using namespace std;
//kaewasuretyuui
typedef long long ll;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<pii> vp;
typedef vector<vp> vvp;
typedef vector<string> vs;
typedef vector<double> vd;
typedef tuple<int,int,int> tp;
typedef vector<tp> vt;
typedef vector<vd> vvd;
typedef pair<int,pii> pip;
typedef vector<pip>vip;
const double PI=acos(-1);
const double EPS=1e-7;
const int inf=1e9;
const ll INF=1e16;
int dx[]={0,1,0,-1,0,2,0,-2};
int dy[]={1,0,-1,0,2,0,-2,0};
int main(){
	int n,m;
	cin>>n>>m;
	int a,b;
	cin>>a>>b;
	int A,B;
	int t=(a-1)/m;
	if(t%2==0){
		A=(a-1)%m+1;
	}else{
		A=m-(a-1)%m;
	}
	t=(b-1)/m;
	if(t%2==0){
		B=(b-1)%m+1;
	}else{
		B=m-(b-1)%m;
	}
	if(A==B)cout<<"YES"<<endl;
	else cout<<"NO"<<endl;
}