#include <iostream>
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 >= m) x = 2 * m - (x + 1);
	if(y >= m) y = 2 * m - (y + 1);
	cout << (x == y ? "YES" : "NO") << endl;
}