import math

ans = 0

N=int(input())
P = []
for i in range(N):
  x, y = map(int, input().split())
  P.append((x, y))

point_info = dict()

for i in range(N):
  for j in range(i+1, N):
    if P[i]==P[j]: continue
    x1, y1 = P[i]
    x2, y2 = P[j]

    tyuten_x = [x1+x2, 2]
    if (x1+x2)%2==0:
      tyuten_x = [(x1+x2)//2, 1]
    tyuten_x = tuple(tyuten_x)

    tyuten_y = [y1+y2, 2]
    if (y1+y2)%2==0:
      tyuten_y = [(y1+y2)//2, 1]
    tyuten_y = tuple(tyuten_y)

    tyuten = (tyuten_x, tyuten_y)

    # 方向 vec
    vec = [x1-x2, y1-y2]
    if vec[1]<0: vec[0]*=-1; vec[1]*=-1
    if x1-x2==0:
      vec[1] = abs(vec[1])
    if y1-y2==0:
      vec[0] = abs(vec[0])
    g = math.gcd(abs(vec[0]), abs(vec[1]))
    vec[0]//=g; vec[1]//=g

    vec = tuple(vec)

    if point_info.get((tyuten_x, tyuten_y, vec))==None:
      point_info[(tyuten_x, tyuten_y, vec)] = 0
    point_info[(tyuten_x, tyuten_y, vec)] += 1



for key in point_info:
  tyuten_x, tyuten_y, (vec_0, vec_1) = key
  inv_vec = [-vec_1, vec_0]

  if inv_vec[1]<0:
    inv_vec[0]*=-1; inv_vec[1]*=-1

  if inv_vec[0]==0:
    inv_vec[1]=abs(inv_vec[1])
  if inv_vec[1]==0:
    inv_vec[0]=abs(inv_vec[0])

  inv_vec = tuple(inv_vec)

  if point_info.get((tyuten_x, tyuten_y, inv_vec))!=None:
    ans += point_info[(tyuten_x, tyuten_y, inv_vec)]



print(ans//2)

# print(point_info)