003. Collections namedtuple().py

# Problem: https://www.hackerrank.com/challenges/py-collections-namedtuple/problem
# Score: 20


from collections import namedtuple


n, Student = int(input()), namedtuple('Student', input())
print("{:.2f}".format(sum([int(Student(*input().split()).MARKS) for _ in range(n)]) / n))