N, = map(int, input().split())
X = []
for i in range(N):
    a, b = map(int, input().split())
    X.append((a, b))
K = []
for i in range(N):
    x, y = X[i]
    for j in range(i+1, N):
        z, w = X[j]
        r = (x-z)**2+(y-w)**2
        K.append((i, j, r))
K.sort(key=lambda x:x[2])
vs = set()
R = 0
for i, j, r in K:
    if i not in vs and j not in vs:
        if i == 0:
            vs.add(j)
            R += 1
        else:
            vs.add(i)
            vs.add(j)
print(R)