// Arup Guha
// 1/27/2018
// Solution to 2017 MCPC Problem B: Batter Up

import java.util.*;

public class batterup {

	public static void main(String[] args) {

		Scanner stdin = new Scanner(System.in);
		int n = stdin.nextInt();
		int bases = 0, atbats = 0;

		// Go through input.
		for (int i=0; i<n; i++) {

			// Ignore walks.
			int num = stdin.nextInt();
			if (num == -1) continue;

			// Count everything else.
			bases += num;
			atbats++;
		}

		// Ta da!
		System.out.println((double)bases/atbats);
	}
}