import sys
input=sys.stdin.readline
def I(): return int(input())
def MI(): return map(int, input().split())
def LI(): return list(map(int, input().split()))



N=I()

if N==1:
    print(0)
    exit()
if N==2:
    print(1)
    exit()

X=[0]*N
Y=[0]*N
for i in range(N):
    X[i],Y[i]=MI()

# 取り除いた or 消えた
used=[0]*N

import heapq
hq=[]
for i in range(N):
    for j in range(i+1,N):
        d=(X[i]-X[j])**2 + (Y[i]-Y[j])**2
        heapq.heappush(hq,(d,i,j))

ans=0
while hq:
    _,i,j=heapq.heappop(hq)
    if i==0:
        if used[j]==0:
            ans+=1
            used[j]=1
    if used[i]==0 and used[j]==0:
        used[i]=1
        used[j]=1
        
print(ans)