#include<bits/stdc++.h>

using namespace std;

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