#include<bits/stdc++.h>
#define int long long
#define fr first
#define sc second
using namespace std;
int const N=1e6+5;
typedef pair<int,int> pii;
int n, m, x, y;

signed main() {
	ios::sync_with_stdio(0);
	cin.tie(0), cout.tie(0);
	cin >> n >> m >> x >> y;

	int p = 2 * m;
	int nx = x % p;
	if (nx == 0) nx = p;
	int ny = y % p;
	if (ny == 0) ny = p;
	if (nx == ny || nx + ny == p + 1) {
		cout << "YES";
	} else {
		cout << "NO";
	}
	return 0;
}