# this passes all but Test Case 7
# now let's try to crak the test cases
# ;)


def distances(pegs):
    l = len(pegs) - 1
    return [pegs[i+1] - pegs[i] for i in range(l)]

def poop(pegs):

    l = len(pegs) - 1

    def solve(pegs):
        d = distances(pegs)
        m = len(d) - 1
        sign = 1

        g = [0 for i in range(l)]

        # this is what elimination turns out to be
        for i in range(m):
            sign *= -1
            d[i+1] -= d[i]

        # get our first value
        x = d[-1]
        g[0] = x/(sign + 0.5)

        # and the rest of them!
        d = distances(pegs)
        for i in range(m):
            g[i+1] = d[i] - g[i]

        return g, sign

    def check(g):
        # gears ain't NEGATIVE
        for i, x in enumerate(g):
            if x <= 0:
                # print 'Negative gear:', i, x
                return False

        if g[0] < 1 and abs(g[0] - 1.0) > 0.01:
            # print 'Too small'
            return False

        return True

    def fraction(ans, sign):
        if sign == -1:
            return [int(round(ans)), 1]

        elif sign == 1:
            # .33333 vs .00001
            if abs(ans - round(ans)) < 0.01:
                return [int(round(ans)), 1]
            else:
                return [int(round(3*ans)), 3]

    gears, sign = solve(pegs)
    ans = gears[0]

    if check(gears):
        return fraction(ans, sign)
    else:
        return [-1, -1]

def answer(pegs):
    correct_answer = poop(pegs)
    return correct_answer