import sys
input = sys.stdin.readline
n=int(input())
p=[tuple(map(int,input().split())) for _ in range(n)]
a=[]
for i in range(n):
    for j in range(i+1,n):
        d=(p[i][0]-p[j][0])**2+(p[i][1]-p[j][1])**2
        a.append((d,i,j))
a.sort()
ans=0
used=[False]*n
for dst,i,j in a:
    if i==0:
        if not used[j]:
            ans+=1
            used[j]=True
    elif not used[j] and not used[i]:
        used[i]=used[j]=True
print(ans)