var
  a, b: integer;

begin
  readln(a);
  while (inttostr(a).Length > 1) do
  begin
    b := 0;
    foreach c: char in inttostr(a) do
      b += strtoint(c);
    a := b;
  end;
  writeln(b);
end.
=======================
var
  a, b, e: integer;
  d: string;

begin
  readln(a);
  d := inttostr(a);
  while (length(d) > 1) do
  begin
    d := inttostr(a);
    b := 0;
    for e := 1 to length(d) do
      b += strtoint(d[e]);
    a := b;
  end;
  writeln(b);
end.