var n,i:integer;
a:string;
sr:real;
begin
readln(a);
n:=0;
sr:=0;
for i:=1 to length(a) do
if a[i] in ['2'..'5'] then begin
  sr+=strtoint(a[i]);
  n+=1;
  end;
sr/=n;
writeln(sr:2:1);
end.