program p1;
var
x, c, i, lens : Longint;
s : String;
begin
c := 10;
Read(x);
Str(x, s);
lens := Length(s);
for i:=1 to lens do
begin
case s[i] of
'1' : if c > 1 then c := 1;
'3' : if c > 3 then c := 3;
'5' : if c > 5 then c := 5;
'7' : if c > 7 then c := 7;
'9' : if c > 9 then c := 9;
end;
end;
if c < 10 then Writeln(c);
end.
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