#28306: CPP 廢話太多
11030067@mail.hpsh.tp.edu.tw
(和平110級鄧雨珊)
#include <iostream>
using namespace std;
int f(int a){
if (a<10){
return a;
}
int sum=0;
while (a>0){
sum+=a%10;
a/=10;
}
return f(sum);
}
int main() {
int n;
while (cin >> n){
if (n==0){
break;
}
cout << f(n) <<endl;
}
}