#include <iostream>

void solve() {
    int n, m, x, y;
    std::cin >> n >> m >> x >> y;
    --x, --y;

    auto id = [&](int v) -> int {
        v %= m * 2;
        return v < m ? v : m * 2 - 1 - v;
    };

    std::cout << (id(x) == id(y) ? "YES" : "NO") << std::endl;
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    solve();

    return 0;
}