#include <string.h>
 
#define M 1000000
 
int main(void)
{
    long long a, b;
    char s[M+1];
    int i;
 
    while (scanf("%s", s) != EOF)
    {
        if (strcmp(s, "0") == 0)
            break;
 
        a = 0;
        for (i=0; s[i]; i++)
            a += s[i]-'0';
 
        while (a>=10)
        {
            b = 0;
            while (a)
            {
                b += a%10;
                a /= 10;
            }
            a = b;
        }
 
        printf("%lld\n", a);
    }
 
    return 0;
}```