import sys
import pypyjit
import itertools
import heapq
import math
from collections import deque, defaultdict
import bisect

input = sys.stdin.readline
sys.setrecursionlimit(10 ** 6)
pypyjit.set_param('max_unroll_recursion=-1')


def index_lt(a, x):
    'return largest index s.t. A[i] < x or -1 if it does not exist'
    return bisect.bisect_left(a, x) - 1


def index_le(a, x):
    'return largest index s.t. A[i] <= x or -1 if it does not exist'
    return bisect.bisect_right(a, x) - 1


def index_gt(a, x):
    'return smallest index s.t. A[i] > x or len(a) if it does not exist'
    return bisect.bisect_right(a, x)


def index_ge(a, x):
    'return smallest index s.t. A[i] >= x or len(a) if it does not exist'
    return bisect.bisect_left(a, x)


N = int(input())
C = [tuple(map(int, input().split())) for _ in range(N)]

h = []
for i in range(N):
    for j in range(i + 1, N):
        xi, yi = C[i]
        xj, yj = C[j]
        d = (xi - xj) ** 2 + (yi - yj) ** 2
        heapq.heappush(h, (d, (i, j)))

S = {i for i in range(N)}
ans = 0
while len(S) > 1:
    _, (a, b) = heapq.heappop(h)
    if a in S and b in S:
        if a == 0:
            S.remove(b)
            ans += 1
        else:
            S.remove(a)
            S.remove(b)
print(ans)