# Uva .11332 - Summing Digits
[**題目連結**](https://onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=2307)

#include<bits/stdc++.h>
#define pii pair<int,int>
#define pll pair<long,long>
#define ll long long
using namespace std;
string f(string s)
{
    int n = 0;
    string temp = "";
    for(auto &c : s)
        n += c - '0';
    temp = to_string(n);
    if(temp.size() == 1)
        return temp;
    else
        return f(temp);
}
int main()
{
    ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    string s;
    while(cin >> s && s != "0")
        cout << f(s) << "\n";

    return 0;
}