from bisect import bisect
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')
    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])
        l, r = sorted(A[:i]), sorted(A[i+1:])
        if l[-1] > A[i] < r[-1]:
            x, y = bisect(l, A[i]), bisect(r, A[i])
            ans = min(ans, l[x] + A[i] + r[y])
    if isinstance(ans, float):
        print(-1)
    else:
        print(ans)


main()