/*
 * Copyright (c) 1999 Johnny C. Lam.
 * All rights reserved.
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  The author makes no representations
 * about the suitability of this software for any purpose.  It is
 * provided "as is" without express or implied warranty.
 */

#include <iostream>
#include <iterator>

using std::cin;
using std::cout;
using std::istream_iterator;

int
main ()
{
    istream_iterator<double> f (cin);
    double sum = 0.0;
    unsigned int num_elements = 0;

    while (f != istream_iterator<double> ()) {
	sum += *f;
	++num_elements;
	++f;
    }
    cout << (sum / num_elements) << endl;

    return 0;
}
