#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,m,x,y,cx,cy;cin>>n>>m>>x>>y;
	int ax=x/m,ay=y/m,bx=x%m,by=y%m;
	if(bx==0)cx=(ax&1?m:1);
	else cx=(ax&1?m-bx+1:bx);
	if(by==0)cy=(ay&1?m:1);
	else cy=(ay&1?m-by+1:by);
	if(cx==cy)cout<<"YES";
	else cout<<"NO";
	return 0;
}