#include<stdio.h>
int main()
{
  long int n,sum;

  while(1)
  {
  	scanf("%ld",&n);
    if(n==0)break;
    while(n/10)
    {
      sum=0;
      while(n)
      {
        sum+=n%10;
        n/=10;
      }
      n=sum;
    }
    printf("%ld\n",n);
  }
  return 0;
}