{programmer:mogtaba amirzade 
url http:\\www.ifjam.com
}
program p18(input,output); {21:repeat form}
var
n,x,j,s:integer;
a:real;
begin
assign(input,'a:\programs\inp18.dat');
reset(input);
assign(output,'a:\programs\outp18.dat');
rewrite(output);
s:=0;
n:=1;
readln(x);
repeat
s:=s+x;
readln(x);
n:=n+1;
until x=9999;
a:=s/n;
writeln(a:1);
readln
end.