#include <bits/stdc++.h>
using namespace std;

#define int long long

int N, M, X, Y;

int GetClass(int n)
{
	int res = (n - 1) % M;
	if ((n - 1)/M&1) res = M - 1 - res;
	return res + 1;
}

signed main()
{
	cin >> N >> M >> X >> Y;
	if (GetClass(X) == GetClass(Y)) puts("YES");
	else puts("NO");
	return 0;
}