eHazi q/27975

from itertools import combinations

def f():
    p = set()
    n = int(input())
    out = 0
    input() #mert van ott egy random üres sor
    for i in range(n):
        p.add(int(input()))
    for subset in combinations(p, 4):
        s = sorted(subset)
        if s[0] + s[3] == s[1] + s[2]:
            out += 1
    return out