var
Str1,c : string;
l,i : integer;
r : boolean;
begin
readln (Str1);
r := true;
i := 1;
l := Length (Str1);
While (r) and (i <= l) do <br>begin
c := copy (Str1,i,1);
if (c <> '1') and (c <> '0') then
r := false;
i := i + 1;
end;
if r then
{writeln ('Ok')}
else
writeln ('Недопустимый символ!');
end.