using System;

public class Moyenne
{
	public static void Main()
	{
		int x = 0, n = 0, sum = 0;
		int[] tab = new int[100];

		try
		{
			string st = Console.ReadLine();
			x = int.Parse(st);

			while( x >= 0 )
			{
				tab[n] = x;
				n++;
				st = Console.ReadLine();
				x = int.Parse(st);
			}
			int length = n;

			for(int i = 0; i < length; i++)
			{
				sum += tab[i];
			}
			float moy = (float)sum / length;
			Console.Out.WriteLine("{0:N2}",moy);
		}

		catch (Exception e)
		{
			Console.Out.WriteLine("Entrée invalide !");
		}
	} // main()
} // class Moyenne