from collections import defaultdict
from itertools import combinations
from math import gcd
N = int(input())
X, Y = map(list, zip(*[map(int, input().split()) for _ in range(N)]))

def compress(dx, dy):
    if dx == 0:
        return (0, 1)
    if dy == 0:
        return (1, 0)
    if dx < 0:
        dx, dy = -dx, -dy
    g = abs(gcd(dx, dy))
    return (dx // g, dy // g)

d = defaultdict(int)
for a, b in combinations(zip(X, Y), 2):
    x1, y1 = a
    x2, y2 = b
    d[(x1 + x2, y1 + y2, compress(x1 - x2, y1 - y2))] += 1

ans = 0
for a, b in combinations(zip(X, Y), 2):
    x1, y1 = a
    x2, y2 = b
    ans += d[(x1 + x2, y1 + y2, compress(y2 - y1, x1 - x2))]
print(ans // 2)