import sys
input = sys.stdin.readline


def dist(a, b):
    return (a[0] - b[0])**2 + (a[1] - b[1])**2

N = int(input())
pts = [tuple(map(int, input().split())) for _ in range(N)]
edges = []
for i in range(N - 1):
    for j in range(i + 1, N):
        edges.append((dist(pts[i], pts[j]), i, j))
edges.sort(key=lambda x: x[0])
removed = [False] * N
ans = 0
for _, i, j in edges:
    if removed[i] or removed[j]:
        continue
    if i == 0:
        removed[j] = True
        ans += 1
    else:
        removed[i] = removed[j] = True
print(ans)