def main():
    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()

    M=10**3+1
    M2=M*M

    def enc(d,i,j):
        temp=d*M2 + i*M + j
        return temp

    def dec(temp):
        d,ij=divmod(temp,M2)
        i,j=divmod(ij,M)
        return d,i,j




    # 取り除いた or 消えた
    used=[0]*N

    L=[0]*(N*(N-1)//2)
    k=0

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

    ans=0
    L.sort()
    S=0

    for aaa in L:
        _,i,j=dec(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()