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

int main () {
    int N, M, X, Y;
    cin >> N >> M >> X >> Y;

    int x = (X - 1) % (2 * M);
    int y = (Y - 1) % (2 * M);

    if (x == y) cout << "YES" << endl;
    else {
        if (x < y && 2 * M - 1 - y == x && x < M && y > M - 1) cout << "YES" << endl;
        else if (x > y && 2 * M - 1 - x == y && x > M  -1 && y < M) cout << "YES" << endl;
        else cout << "NO" << endl;
    }

    return 0;
}