from sys import stdin


def main():
    input = lambda: stdin.readline()[:-1]
    N = int(input())
    A = list(map(int, input().split()))

    left, right = [A[0]], [A[-1]]
    min_ = A[0]
    for i in range(1, N):
        n = min(min_, A[i])
        left.append(n)
        min_ = n
    min_ = A[-1]
    for i in range(N - 2, -1, -1):
        n = min(min_, A[i])
        right.append(n)
        min_ = n
    right = right[::-1]

    ans = float('inf')
    a = A[:]
    n = min(a)
    while 1:
        if n == float('inf'):
            break
        i = a.index(n)
        if not i or i == N - 1:
            a[i] = float('inf')
        elif a[i-1] == float('inf') or a[i+1] == float('inf'):
            a[i] = float('inf')
        else:
            break
        n = min(a)
    if n != float('inf'):
        ans = min(a[:i]) + a[i] + min(a[i+1:])
    for i in range(1, N - 1):
        if left[i-1] < A[i] > right[i+1]:
            ans = min(ans, left[i-1] + A[i] + right[i+1])
    if isinstance(ans, float):
        print(-1)
    else:
        print(ans)


main()