N = int(input())
A = [list(map(int, input().split())) for _ in range(N)]
seen = [0]*N

task = []
for i in range(N):
    xi, yi = A[i]
    for j in range(i+1, N):
        xj, yj = A[j]
        task.append([(xi-xj)**2+(yi-yj)**2, i, j])

task.sort()
ans = 0
for _, indi, indj in task:
    if seen[indi] | seen[indj]:
        continue
    if indi > 0:
        seen[indi] = seen[indj] = 1
    else:
        ans += 1
        seen[indj] += 1

print(ans)