aipo final 2013 q3

q3.py

n = int(raw_input())
a = [ int(raw_input()) for x in range(n) ]
average_count = 0

for (i, el) in enumerate(a):
    a.pop(i) # remove that element
    for to_avg_with in a:
        avg = (el + to_avg_with) / 2
        if avg in a:
            average_count += 1

print(average_count)