from collections import namedtuple
#take in the input
people = [input().split() for i in range(int(input())+1)]
heading = ''
#to get the second parameter in the namedtuple
for i in people[0]:
    heading=heading + i +' '

total = 0
#defining the named_tuple
students = namedtuple('students', heading)

#calculating the total
for i in range(1, len(people)):
    temp_tuple = students(people[i][0],people[i][1], people[i][2], people[i][3])
    total = total+ int(temp_tuple.MARKS)
to_divide = len(people)-1
#printing out the average
print(float(total/to_divide))