#include<bits/stdc++.h>
using namespace std;
int n,m,x,y,X,Y;
int main()
{
	cin>>n>>m>>x>>y;
	X=(x-1)%(2*m)+1;
	Y=(y-1)%(2*m)+1;
	if(X==Y||X+Y==2*m+1)cout<<"YES";
	else cout<<"NO";
}