# collections.namedtuple()
# Basically, namedtuples are easy to create, lightweight object types.
# They turn tuples into convenient containers for simple tasks.
# With namedtuples, you don’t have to use integer indices for accessing members of a tuple.

# Example
# Code 01

# >>> from collections import namedtuple
# >>> Point = namedtuple('Point','x,y')
# >>> pt1 = Point(1,2)
# >>> pt2 = Point(3,4)
# >>> dot_product = ( pt1.x * pt2.x ) +( pt1.y * pt2.y )
# >>> print dot_product
# 11

# Code 02

# >>> from collections import namedtuple
# >>> Car = namedtuple('Car','Price Mileage Colour Class')
# >>> xyz = Car(Price = 100000, Mileage = 30, Colour = 'Cyan', Class = 'Y')
# >>> print xyz
# Car(Price=100000, Mileage=30, Colour='Cyan', Class='Y')
# >>> print xyz.Class
# Y

# Task

# Dr. John Wesley has a spreadsheet containing a list of student's
# IDs, marks, class and name.

# Your task is to help Dr. Wesley calculate the average marks of the students.

# Average = Sum of all marks / Total Students

# Note:
# 1. Columns can be in any order. IDs, marks, class and name can be written in any order in the spreadsheet.
# 2. Column names are ID, MARKS, CLASS and NAME. (The spelling and case type of these names won't change.)

# Input Format
# The first line contains an integer N, the total number of students.
# The second line contains the names of the columns in any order.
# The next N lines contains the marks, IDs, name and class, under their respective column names.

# Output Format
# Print the average marks of the list corrected to 2 decimal places.

# Sample Input

# TESTCASE 01
# 5
# ID         MARKS      NAME       CLASS     
# 1          97         Raymond    7         
# 2          50         Steven     4         
# 3          91         Adrian     9         
# 4          72         Stewart    5         
# 5          80         Peter      6   

# TESTCASE 02
# 5
# MARKS      CLASS      NAME       ID        
# 92         2          Calum      1         
# 82         5          Scott      2         
# 94         2          Jason      3         
# 55         8          Glenn      4         
# 82         2          Fergus     5

# Sample Output
# TESTCASE 01
# 78.00

# TESTCASE 02
# 81.00

# Explanation
# TESTCASE 01

# Average = (97 + 50 + 91 + 72 + 80)/5
# Can you solve this challenge in 4 lines of code or less?
# NOTE: There is no penalty for solutions that are correct but have more than 4 lines.

from collections import namedtuple

n = int(input())
marks = 0
l = list(map(str,input().split()))
student = namedtuple('student', l)._make(range(4))
for i in range(n):
    info = list(map(str, input().split()))
    add_marks = info[student.MARKS]
    marks += int(add_marks)
average = marks / n
print("%.2f" %(average))