HDU 1013

include<stdio.h>
#include<string.h>
int main()
{
    int sum,i,n;
    char s[10000];
    gets(s);
    while(strcmp(s,"0"))
    {
        sum=0;
        for(i=0;i<strlen(s);i++)
            sum+=s[i]-'0';
        while(sum/10)
        {
            n=sum;
            sum=0;
            while(n!=0)
            {
                sum+=n%10;
                n/=10;
            }
        }
        printf("%d\n",sum);
        gets(s);
    }
}