N = int(input()) x = [None] * N y = [None] * N for i in range(N): x[i], y[i] = map(int, input().split()) INF = 10 ** 12 burst = [] for i in range(N): for j in range(i + 1, N): res = (x[j] - x[i]) ** 2 + (y[j] - y[i]) ** 2 burst.append((res, i, j)) burst.sort() baloon = set() cnt = 0 for b, i, j in burst: if i in baloon or j in baloon: continue if i == 0: cnt += 1 baloon.add(j) continue else: baloon.add(i) baloon.add(j) print(cnt)