n=int(input())
X=[0]*n
Y=[0]*n
import sys
input=sys.stdin.readline #文字列入力はするな！

for i in range(n):
    x,y=map(int,input().split())

    X[i]=x
    Y[i]=y
ans=0

dis=[]

for i in range(n-1):
    for j in range(i+1,n):
        xi,yi,xj,yj=X[i],Y[i],X[j],Y[j]
        dis.append(((xi-xj)**2+(yi-yj)**2,i,j))

dis=sorted(dis,key=lambda x: x[0])
erase=[0]*(n)
for d,p,q in dis:

    if p==0:
        if erase[q]==0:
            ans+=1
            erase[q]=1
    else:
        if erase[p]==erase[q]==0:
            erase[p] = erase[q]=1

print(ans)