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.