def main():
    N = int(input())
    lsxy = [tuple(map(int,input().split())) for i in range(N)]
    ls = []
    for i in range(N-1):
        for j in range(i+1,N):
            dist = (lsxy[i][0]-lsxy[j][0])**2 + (lsxy[i][1]-lsxy[j][1])**2
            ls.append((dist,i,j))
    ls.sort()
    ans = 0
    used = [False]*N
    for d,a,b in ls:
        if a == 0 and used[b] == False:
            used[b] = True
            ans += 1
        elif used[a] or used[b]:
            continue
        else:
            used[a] = True
            used[b] = True
    print(ans)
main()