#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;

	if(x < 2*m){
		x -= 1;
	}else{
		x = x % (2*m);		
	}
	if(y < 2*m){
		y -= 1;
	}else{
		y = y % (2*m);		
	}


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