llong vert_summ(int **arr, int n) {
        assert (arr != NULL);
        assert (n > 0);
        assert (n % 2 == 1);

        int middle = n / 2;
        llong summ = 0;
        for (int i = 0; i != n; ++i) {
                summ += arr[i][middle];
        }
        return summ;
}

llong left_diag(int **arr, int n) {
        assert (arr != NULL);
        assert (n > 0);
        assert (n % 2 == 1);

        llong summ = 0;
        for (int i = 0; i != n; ++i) {
                summ += arr[i][i];
        }
        return summ;
}

llong right_diag(int **arr, int n) {
        assert (arr != NULL);
        assert (n > 0);
        assert (n % 2 == 1);

        llong summ = 0;
        for (int i = 0; i != n; ++i) {
                summ += arr[i][n-i];
        }
        return summ;
}

llong sum2(int **arr, int n) {
        assert (arr != NULL);
        assert (n > 0);
        assert (n % 2 == 1);

        int middle = n / 2;
        return vert_summ(arr, n) + right_diag(arr, n) - arr[middle][middle];
}

llong sum2_opt(int **arr, int n) {
        assert (arr != NULL);
        assert (n > 0);
        assert (n % 2 == 1);

        int middle = n / 2;
        llong vert_summ = 0;
        llong right_diag = 0;
        for (int i = 0; i != n; ++i) {
                vert_summ += arr[i][middle];
                right_diag += arr[i][n-i];
        }
        return vert_summ + right_diag - arr[middle][middle];
}