ITSA11

#include<stdio.h>
#include<stdlib.h>
int main(){
int n;
while(scanf("%d",&n)==1){
    if(n==0) break;
    while(n>=10){
        int sum=0;
        while(n!=0){
            sum+=n%10;
            n/=10;
        }
        n=sum;
    }
    printf("%d\n",n);
}
return 0;
}