#include <bits/stdc++.h>
using namespace std;
int n,m,x,y; 
signed main ()
{
	cin>>n>>m;
	cin>>x>>y;
	if (x>=2*m) x%=2*m;
	if (y>=2*m) y%=2*m;
	if (x==0) x+=m;
	if (y==0) y+=m;
	if (x==y||x+y==2*m+1) cout<<"YES\n";
	else cout<<"NO\n";
	return 0;
}