#include<iostream>
#include<cmath>
#include<algorithm>
using namespace std;

int main(){
    int n,m,x,y;
    cin>>n>>m>>x>>y;
    if((x-1)/m%2==(y-1)/m%2){
        if(x%m==y%m) cout<<"YES"<<endl;
        else cout<<"NO"<<endl;
        return 0;
    }else{
        int rev=((x-1)/m%2==1)?x:y;
        int nonrev=(rev==x)?y:x;
        if(nonrev%m==abs(rev%m-m-1)%m) cout<<"YES"<<endl;
        else cout<<"NO"<<endl;
        return 0;
    }
    cout<<"NO"<<endl;
    return 0;
}