def on_one_line(x1, y1, x2, y2, x3, y3):
    return (x1 - x2) * x3 + (y1 - y2) * y3 == 0


def rotate(A, B, C):
    return (B[0] - A[0]) * (C[1] - B[1]) - (B[1] - A[1]) * (C[0] - B[0])


def jarvismarch(A):
    n = len(A)

    counter = 0

    P = [i for i in range(n)]

    for i in range(1, n):
        if A[P[i]][0] < A[P[0]][0]:
            P[i], P[0] = P[0], P[i]

    H = [P[0]]
    del P[0]
    P.append(H[0])

    while True:
        right = 0
        for i in range(1, len(P)):

            if rotate(A[H[-1]], A[P[right]], A[P[i]]) < 0:
                right = i

        if P[right] == H[0]:
            break

        else:
            if on_one_line(A[H[-3]][0], A[H[-3]][1], A[H[-2]][0], A[H[-2]][1], A[H[-1]][0], A[H[-1]][1]):
                counter += 1
            H.append(P[right])
            del P[right]
    return len(H) - counter


n = int(input())
A = []
point = [0, 0]
for i in range(n):
    A.append([int(el) for el in input().split()])
print((n - 1) * jarvismarch(A))