n=int(input())
xy=[list(map(int,input().split()))for _ in range(n)]
e=[]
for i in range(n-1):
  for j in range(i+1,n):
    x1,y1=xy[i]
    x2,y2=xy[j]
    e.append(((x1-x2)**2+(y1-y2)**2,i,j))
e.sort()
used=[0]*n
ans=0
for _,i,j in e:
  if used[i]+used[j]:
    continue
  if i==0:
    used[j]=1
    ans+=1
  else:
    used[i]=used[j]=1
print(ans)