#include <iostream>
#include <string>

using namespace std;

int main()
{
    string str;
    while (cin >> str && str.empty() == false && str[0] != '0')
    {
        int n = 0,sum = 0;
        for (int i = 0;i < str.size();i++)
        {
            n += str[i] - '0';
        }

        while (n != 0 || ((sum / 10) != 0 ?n = sum,sum = 0,1 : 0))
        {
            
            sum += n % 10;
            n = n / 10;
        }
        cout << sum << endl;
    }
    return 0;
}