N=int(input())
F=[tuple(map(int,input().split())) for i in range(N)]

LIST=[]

for i in range(N):
    x,y=F[i]
    for j in range(i+1,N):
        z,w=F[j]

        LIST.append(((x-z)**2+(y-w)**2,i,j))

LIST.sort()
ANS=0
USE=[0]*N

for d,i,j in LIST:
    if USE[i]==1 or USE[j]==1:
        continue
    if i==1:
        ANS+=1
        USE[j]=1
    else:
        USE[i]=1
        USE[j]=1
        
print(ANS)