#include <bits/stdc++.h>
#define p(s) cout<<(s)<<endl
using namespace std;

int main() {
	int N,M,X,Y;
	cin >> N >> M >> X >> Y;
	X--;
	Y--;
	X%=2*M;
	Y%=2*M;
	if((X==Y)||(X+Y+1==2*M)) p("YES");
	else p("NO");
	return 0;
}