#include<stdio.h>
#include<string.h>
int root2(char *s)
{
int sum2 = 0;
int i, len = strlen(s);
for(i = 0; i < len; i++)
sum2 += s[i] - '0';
return sum2;
}
long root(long n)
{
long sum = 0;
while(n)
{
sum += n % 10;
n /= 10;
}
return sum;
}
int main()
{
long sum;
char s[1000];
gets(s);
while(strcmp(s, "0"))
{
sum = root2(s);
while(sum / 10)
{
sum = root(sum);
}
printf("%d\n", sum);
gets(s);
}
}



