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()))


def main():
    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

    L=[]

    for i in range(N):
        for j in range(i+1,N):
            d=(X[i]-X[j])**2 + (Y[i]-Y[j])**2
            L.append((d,i,j))

    ans=0
    L.sort(key=lambda x:x[0])
    S=0

    for aaa in L:
        _,i,j=aaa
        if i==0:
            if used[j]==0:
                ans+=1
                used[j]=1
                S+=1
        if used[i]==0 and used[j]==0:
            used[i]=1
            used[j]=1
            S+=2
        if S==N-1:
            break
            
    print(ans)
main()