var r,n:longint;
    c:char;
begin
 read(c);
 while c>'0' do
  begin
   r:=0;
   n:=0;
   while (c<='9')and(c>='0') do
    begin
     n:=n+ord(c)-ord('0');
     read(c);
    end;
   while n>0 do
    begin
     while n>0 do
      begin
       r:=r+n mod 10;
       n:=n div 10;
      end;
     if r>9 then
      begin
       n:=r;
       r:=0;
      end;
    end;
   writeln(r);
   readln;
   read(c);
  end;
end.