scientific_comp_projects/CODE/[python]kattis/trivial/batter_up.py

n = int(input())

cases = input()
cases = cases.split(' ')

valid = 0
nb = 0
for i in range(n):
    value = int(cases[i])
    if value !=-1:
        valid += value
        nb += 1

points = valid / nb
print(points)