import heapq
N = int(input())
A = [int(a) for a in input().split()]

ans = 10**9
l = A[0]
h = []
for i in range(2, N):
    heapq.heappush(h, (A[i], i))

for i in range(1, N-1):
    while len(h) > 0 and h[0][1] <= i:
        heapq.heappop(h)
    if len(h) == 0:
        break
    if l < A[i] and h[0][0] < A[i]:
        ans = min(ans, l+A[i]+h[0][0])
    elif A[i] < l and A[i] < h[0][0]:
        ans = min(ans, l+A[i]+h[0][0])
    l = min(l, A[i])

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