str2num.fun

int binpow(int n, int m)
{
    if (m == 0)
        return 1;
    if (m == 1)
        return n;
    int tmp = binpow(n, m/2);
    if (m % 2)
        return tmp*tmp*n;
    else
        return tmp*tmp;
}

int str2num(string str)
{
    int num = 0;
    for (int i = 0; i < (int)str.size(); ++i)
        num += (str[i] - '0')*binpow(10, str.size()-i-1);
    return num;
}