#include<iostream>
#include<string>
using namespace std;
int main()
{
	string str;
	while(cin>>str&&str!="0")
	{
	 int long1;
	 int sum=0;
	 long1=str.length();
	 for(int i=0;i<long1;i++)
	 {
	  sum+=int(str[i]-'0');
	 if(sum>=10)
	  sum=sum-9;	 
	 }
	cout<<sum<<endl;

	}
 return 0;
}