<stdin>

function int unusedTID(int start, int end)
{
    int ret = start - 1;
    int tidNum;

    if (start > end) { start ^= end; end ^= start; start ^= end; }  // good ol' XOR swap

    while (ret++ != end)
    {
        if (ThingCount(0, ret) == 0)
        {
            return ret;
        }
    }

    return -1;
}