N = int(input())
x = [0] * N
y = [0] * N
for i in range(N):
    x[i],y[i] = map(int,input().split())
l = []
for i in range(N):
    for j in range(i+1,N):
        s = (x[i]-x[j]) ** 2
        t = (y[i]-y[j]) ** 2
        l.append((s+t,i,j))
l.sort(key = lambda x:x[0])
s = set()
ans = 0
for d,i,j in l:
    if i == 0 or j == 0:
        if j == 0:
            i,j = j,i
        if j not in s:
            ans += 1
            s.add(j)
    else:
        if i not in s and j not in s:
            s.add(i)
            s.add(j)
print(ans)