#include <iostream>
using namespace std;

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