package main

import (
	"bufio"
	"fmt"
	"os"
)

func main() {
	in := bufio.NewReader(os.Stdin)
	var x int
	sum := 0.0
	count := 0.0

	for {
		_, err := fmt.Fscan(in, &x)
		if err != nil {
			break
		}
		sum += float64(x)
		count++
	}

	fmt.Printf("%.10f\n", sum/count)
}