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
        l.append([dis,i,j])

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