n = int(input())
xy = [tuple(map(int, input().split())) for _ in range(n)]
dist = []
for i in range(n):
    x1, y1 = xy[i]
    for j in range(i+1, n):
        x2, y2 = xy[j]
        d = (x1-x2)**2+(y1-y2)**2
        dist.append((d, i, j))
dist = sorted(dist, key=lambda x: x[0])
used = set()
res = 0
for _, i, j in dist:
    if i == 0:
        if j in used:
            continue
        else:
            res += 1
            used.add(j)
    else:
        if i in used or j in used:
            continue
        else:
            used.add(i)
            used.add(j)

print(res)