N = int(input())
A = list(map(int, input().split()))
L0 = [A[0]]
L1 = [A[-1]]
for i in range(1, N):
    L0.append(min(L0[-1], A[i]))
    L1.append(min(L1[-1], A[-i - 1]))
L1 = L1[::-1]
ans = INF = 10 ** 9
for i in range(1, N - 1):
    if L0[i - 1] < A[i] and L1[i + 1] < A[i]:
        ans = min(ans, L0[i - 1] + A[i] + L1[i + 1])
mini = A.index(min(A))
if 0 < mini < N - 1:
    ans = min(ans, L0[mini - 1] + A[mini] + L1[mini + 1])
if ans == INF:
    print(-1)
else:
    print(ans)