def is_kadomatsu(a, b, c):
    return len({a, b, c}) == 3 and (b > max(a, c) or b < min(a, c))


def main():
    n = int(input())
    a = list(map(int, input().split()))

    left = [a[0]] * n
    right = [a[-1]] * n
    for i in range(1, n):
        left[i] = min(left[i - 1], a[i])
    for i in reversed(range(n - 1)):
        right[i] = min(a[i], right[i + 1])

    ans = 10 ** 9
    for i in range(1, n - 1):
        if is_kadomatsu(left[i - 1], a[i], right[i + 1]):
            ans = min(ans, left[i - 1] + a[i] + right[i + 1])

    if ans == 10 ** 9:
        ans = -1
    print(ans)


if __name__ == "__main__":
    main()