#include <cstring>
#define max_len 1000
using namespace std;
int num2str(int a,char * b){//return length of a[]
int i=0;
while(a>0){
b[i]=char(a%10+'0');
//cout<<b[i]<<"**";
a/=10;
i++;
}
//b[i]='\0';
char ch;
//cout<<b<<"----"<<endl;
for(int j=0;j<i/2;j++){// reverse the string
ch=b[j];
b[j]=b[i-j-1];
b[i-j-1]=ch;
}
//cout<<b<<"--";
return i;//i==len
}
int main()
{
char a[max_len];
int root,len,sum;
while(1){
cin>>a;
if(a[0]=='0') break;
len=strlen(a);
sum=0;
while(1){
for(int i=0;i<len;i++){
sum+=a[i]-'0';
}
if(sum>9)
len=num2str(sum,a);
if(sum<=9) break;
sum=0;
}
cout<<sum<<endl;//sum is root digit
}
return 0;
}