九度 1124

#include <cstdio>
#include <iostream>
#include <string>
using namespace std;

#ifdef ONLINE_JUDGE                                   
#define FINPUT(file)  0
#define FOUTPUT(file) 0
#else                                                
#define FINPUT(file)  freopen(file,"r",stdin)
#define FOUTPUT(file) freopen(file,"w",stdout)
#endif

unsigned int sumOfDigits(string s)
{
    unsigned int sum = 0;
    int i = 0;
    while(i<s.length())
    {
        sum += s[i]-'0';
        i++;
    }
    return sum;
}

unsigned int sumOfDigits2(unsigned int n)
{
    unsigned int sum = 0;
    while(n!=0)
    {
        sum += n%10;
        n/=10;
    }
    return sum;
}

int main()
{    
	FINPUT("in.txt");
    FOUTPUT("out.txt");

    string s;
    while(cin>>s && s!="0")
    {   
        int sum = sumOfDigits(s);
        while(sum>=10)
        {
            sum = sumOfDigits2(sum);
        }
    	cout<<sum<<endl;
    }
    return 0;
}