ARC 123

void solve() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    ll a, b, c;
    cin >> a >> b >> c;

    ll x = b * 2 - a - c;
    ll ans = 0;
    if (x >= 0) {
        ans = x;
    } else {
        x = abs(x);
        ll q = (x + 1) / 2;
        ll r = x % 2;
        ans = q + r;
    }
    cout << ans << endl;
}