n=int(input())
xy=[list(map(int,input().split())) for _ in range(n)]
ary=[]
#mat=[[0]*n for i in range(n)]
for i in range(n):
  xi,yi=xy[i]
  for j in range(i):
    xj,yj=xy[j]
    d=(xi-xj)**2+(yi-yj)**2
    #mat[i][j]=d
    #mat[j][i]=d
    ary.append([d,i,j])
ary.sort()
ans=0
seen=[0]*n
for d,i,j in ary:
  if seen[i]==0 and seen[j]==0:
    seen[i]=1
    seen[j]=1
    if i==0 or j==0:
      ans+=1
      seen[0]=0

print(ans)