#include <bits/stdc++.h>

#define REP(i, x, n) for (int i = x; i < (int)(n); i++)
#define rep(i, n) REP (i, 0, n)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define sz(x) (int)(x.size())
#define popcount(x) __builtin_popcount(x)
#define popcountll(x) __builtin_popcountll(x)
#define uniq(x) x.erase(unique(x.begin(), x.end()), x.end())
#define F first
#define S second
#define mp make_pair
#define eb emplace_back

using namespace std;

typedef long long ll;

const int INF = 1 << 29;

int main() {
    int n, m, x, y;
    cin >> n >> m >> x >> y;
    int a = x % (2 * m);
    int b = y % (2 * m);
    if (m == 1 || a == b || a + b == 2 * m + 1) {
        cout << "YES" << endl;
    } else {
        cout << "NO" << endl;
    }
}