# A set is an unordered collection of elements without duplicate entries.
# When printed, iterated or converted into a sequence, its elements will appear in an arbitrary order.

# Example

# >>> print set()
# set([])

# >>> print set('HackerRank')
# set(['a', 'c', 'e', 'H', 'k', 'n', 'r', 'R'])

# >>> print set([1,2,1,2,3,4,5,6,0,9,12,22,3])
# set([0, 1, 2, 3, 4, 5, 6, 9, 12, 22])

# >>> print set((1,2,3,4,5,5))
# set([1, 2, 3, 4, 5])

# >>> print set(set(['H','a','c','k','e','r','r','a','n','k']))
# set(['a', 'c', 'r', 'e', 'H', 'k', 'n'])

# >>> print set({'Hacker' : 'DOSHI', 'Rank' : 616 })
# set(['Hacker', 'Rank'])

# >>> print set(enumerate(['H','a','c','k','e','r','r','a','n','k']))
# set([(6, 'r'), (7, 'a'), (3, 'k'), (4, 'e'), (5, 'r'), (9, 'k'), (2, 'c'), (0, 'H'), (1, 'a'), (8, 'n')])
# Basically, sets are used for membership testing and eliminating duplicate entries.

# Task

# Now, let's use our knowledge of sets and help Mickey.

# Ms. Gabriel Williams is a botany professor at District College. One day, she asked her student Mickey to compute the average of all the plants with distinct heights in her greenhouse.

# Formula used:

# Function Description

# Complete the average function in the editor below.

# average has the following parameters:

# int arr: an array of integers
# Returns

# float: the resulting float value rounded to 3 places after the decimal
# Input Format

# The first line contains the integer, , the size of .
# The second line contains the  space-separated integers, .

# Constraints


# Sample Input

# STDIN                                       Function
# -----                                       --------
# 10                                          arr[] size N = 10
# 161 182 161 154 176 170 167 171 170 174     arr = [161, 181, ..., 174]
# Sample Output

# 169.375
# Explanation

# Here, set is the set containing the distinct heights. Using the sum() and len() functions, we can compute the average.






# Soln:
def average(array):
    # your code goes here
    s = set(array)
    avg = sum(s)/len(s)
    return avg

if __name__ == '__main__':
    n = int(input())
    arr = list(map(int, input().split()))
    result = average(arr)
    print(result)