import sys
input = sys.stdin.readline
n = int(input())
xy = [list(map(int,input().split())) for i in range(n)]

l = []
for i in range(n-1):
    for j in range(i+1,n):
        dis = ((xy[i][0]-xy[j][0])**2+(xy[i][1]-xy[j][1])**2)**0.5
        l.append((dis,i,j))

ans = 0
count = [1]*n
l.sort()
su = n
for dis,i,j in l:
    if count[i] == 0 or count[j] == 0:
        continue
    if i != 0:
        count[i] -= 1
        count[j] -= 1
        su -= 2
    if i == 0:
        ans += 1
        count[j] -= 1
        su -= 1
    if su == 1:
        print(ans)
        exit()
print(ans)