text: #!/usr/bin/env python3
  # -*- coding: utf-8 -*-
  """
  @created: 26.06.20
  @author: felix
  """
  from collections import namedtuple
  
  if __name__ == '__main__':
      students = []
      total = int(input().rstrip())
      student = namedtuple('student', input().split())
      [students.append(student(*input().split())) for i in range(total)]
      print(sum(int(s.MARKS) for s in students) / total)
  