#include
using namespace std;
int main()
{
int x;
while(cin>>x)
{
if(x!=0)
{
int sum=0;
while(sum==0 ||sum>=10)
{
sum=0;
while(x>0)
{
sum += x%10;
x = x/10;
}
x=sum;
if(sum>0 && sum<10)
{
cout << sum << endl;
break;
}
}
}
}
return 0;
}