import java.io.*;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.text.DecimalFormat;
import java.util.List;
import java.util.Scanner;
public class t766 {
    public static void main(String[] args) throws Exception{
        FileReader fr = new FileReader ("input.txt");
        FileWriter fw = new FileWriter ("output.txt");
        Scanner in = new Scanner(fr);
        double m=0;
        int i=0;
        List<String> lines = Files.readAllLines(Paths.get("input.txt"), Charset.defaultCharset());
        for (String x:lines)
        {

            m+=Integer.parseInt(lines.get(i));
            i++;

        }
        in.close();
        fr.close();
        String formattedDouble = new DecimalFormat("#0.000").format(m/i);
        fw.write(formattedDouble);

        fw.close();

    }

}