// write your code here cpp
#include<iostream>
#include<string>

using namespace std;

void getResult(int n)
{
    int res = 0;
    while (n)
    {
        res += n % 10;
        n = n / 10;
        if (n == 0 && res / 10 != 0)
        {
            n = res;
            res = 0;
        }
    }
    cout << res << endl;
}

int main()
{
    string str;
    while (cin >> str)
    {
        int n = 0;
        for (int i = 0; i < str.size(); ++i)
        {
            n += str[i] - '0';
        }
        getResult(n);
    }
    return 0;
}