program p1004;
var
  a:array[1..12] of real;
  i:integer;
  sum:real;
begin
  for i:=1 to 12 do
  readln(a[i]);
  for i:=1 to 12 do
  sum:=sum+a[i];
  sum:=sum/12;
  writeln('$',sum:0:2);
end.