n=int(input())
p=[list(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
t=set()
for dst,i,j in a:
    if i in t or j in t:
        continue
    if i==0:
        ans+=1
        t.add(j)
    else:
        t.add(i)
        t.add(j)
print(ans)