void task4() {
    int n;
    cin >> n;
    vector<ll> v(n);
    for (int i = 0; i < n; i++) {
        cin >> v[i];
    }
    ll sum = 0;
    for (int i = 0; i < n; i += 2) {
        int i1 = i + 1;
        int j1 = i1 + 1;
        for (int j = i + 1; j < n; j++) {
            ll s = 0;
            if (abs(v[i] - v[j]) > 1) {
                s = v[j] - v[i];
                sum += s;
            }
            else {
                sum += 0;
            }
            if (j1 < n && i1 < n) {
                s = 0;
                if (abs(v[i1] - v[j1]) > 1) {
                    s = v[j1] - v[i1];
                    sum += s;
                }
                else {
                    sum += 0;
                }
            }
            j1++;
        }
    }
    cout << sum;
}