Collections.namedtuple()

from collections import namedtuple

N = int(input())
order = input().split()
student = namedtuple('student', order)
s = 0
for i in range(N):
    inpu = input().split()
    stu = student(*inpu)
    # print(*inpu)
    s += int(stu.MARKS)
    
print(s/N)