import java.util.*;
import java.lang.*;
import java.io.*;
class Main
{
{
Scanner in
= new Scanner
(System.
in); double sum = 0.0, number = 0.0, x = 1;
while (in.hasNext() && x >= 0) {
x = in.nextDouble();
sum += x;
number++;
}
System.
out.
println(sum
/ number
); }
}
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