int binarysearch(int a, int mass[], int n)
{
    int low, high, middle;
    low = 0;
    high = n - 1;
    while (low <= high)
    {
        middle = (low + high) / 2;
        if (a < mass[middle])
            high = middle - 1;
        else if (a > mass[middle])
            low = middle + 1;
        else
            return middle;
    }
    return -1;
}