import sys
input=sys.stdin.readline
N=int(input())
A=[]
for i in range(N):
  x,y=map(int, input().split())
  A.append((x,y,i))
B=[]
for i in range(N-1):
  for j in range(i+1,N):
    ax,ay,an=A[i][0],A[i][1],A[i][2]
    bx,by,bn=A[j][0],A[j][1],A[j][2]
    d=(ax-bx)**2+(ay-by)**2
    B.append((d,an,bn))
B=sorted(B)
ans=0
D=[1]*N
for i in range(len(B)):
  na,nb=B[i][1],B[i][2]
  if D[na]==1 and D[nb]==1:
    if na==0:
      ans+=1
      D[nb]=0
    else:
      D[na]=0
      D[nb]=0
print(ans)