#include <iostream>
using namespace std;
string a;
int N;
int f(int x)
{
if(x<=9) return x;
else
{
int s=0;
while(x>0)
{
s+=x%10;
x/=10;
}
return f(s);
}
}
int main()
{
while(1)
{
cin>>a;
if(a.length()==1&&a[0]=='0') break;
N=0;
for(int x=0; x<a.length(); x++)
{
N+=a[x]-48;
}
cout<<f(N)<<endl;
}
}