#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(X==0)X=1; if(Y>M){ Y=2*M-Y+1; } if(Y==0)Y=1; //cout<<X<<' '<<Y<<endl; if(X==Y){ cout<<"YES"<<endl; }else{ cout<<"NO"<<endl; } return 0; }