#include <iostream>
#include <stdio.h>
#include <math.h>
#include <vector>
#include <algorithm>
using namespace std;

int main(){

	long long int n,m,x,y;
	cin >> n >> m;
	cin >> x >> y;

	x -= 1;
	y -= 1;

	x = x % (2*m);		
	y = y % (2*m);		

	if( x==y || x+y == (2*m-1) ){
		cout << "YES" << endl;
	}else{
		cout << "NO" << endl;
	}
	
	return 0;
}