import java.util.*;
import java.lang.*;
import java.io.*;

class Main
{
	public static void main (String[] args) throws java.lang.Exception
	{
		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);
	}
}