#include <iostream>
using namespace std;

int main(){
	int n,m,x,y;
	cin >> n >> m >> x >> y;
	int xno = ((x + m - 1) / m & 1 ? (x % m == 0 ? m : (x + 1) % m) : x - x % m),yno = ((y + m - 1) / m & 1 ? (y % m == 0 ? m : (y + 1) % m) : y - y % m);
	cout << (xno == yno ? "YES" : "NO") << endl;
}