uses crt;
var f,f1:text; i,n,max,min:longint; a:array[1..1000000] of longint;
begin
clrscr;
assign(f,'bt4.txt');reset(f);
assign(f1,'bt4.out');rewrite(f1);
while not(eof(f)) do
begin
n:=0; max:=low(longint); min:=high(longint);
while not(eoln(f)) do
begin
inc(n); read(f,a[i]);
if a[i]>max then max:=a[i];
if a[i]<min then min:=a[i];
end;
writeln(f1,(max+min)/2:0:3);
readln(f);
end;
close(f1);
close(f);
end.