N = int(input())
XY = [list(map(int, input().split())) for _ in range(N)]
D = []

for i in range(N - 1):
    x1, y1 = XY[i]
    for j in range(i + 1, N):
        x2, y2 = XY[j]
        d2 = (x1 - x2) ** 2 + (y1 - y2) ** 2
        D.append((d2, i, j))
D.sort()
cnt = 0
removed = set()
for d, i, j in D:
    if i == 0:
        if j in removed:
            continue
        else:
            removed.add(j)
            cnt += 1
    else:
        if i in removed or j in removed:
            continue
        else:
            removed.add(i)
            removed.add(j)
print(cnt)