N = int(input())
A = list(map(int,input().split()))
INF = int(1e9)
min_A = INF
min_pos = 0
for i in range(N):
	if(A[i] < min_A):
		min_A = A[i]
		m_pos = i
min_left = []
ML = INF
for i in range(N):
	ML = min(ML, A[i])
	min_left.append(ML)
min_right = []
MR = INF
for i in range(N):
	MR = min(MR, A[N-1-i])
	min_right.append(MR)
min_right.reverse()
ans = INF
if(m_pos >= 1 and m_pos < N-1):
	ans = min_left[m_pos-1] + min_A + min_right[m_pos+1]
res = INF
for i in range(1, N-1):
	if(i == m_pos): continue
	if(i < m_pos):
		left = min_left[i-1]
		if(left > A[i]): continue
		size = left + A[i] + min_A
		res = min(res, size)
	if(i > m_pos):
		right = min_right[i+1]
		if(right > A[i]): continue
		size = min_A + A[i] + right
		res = min(res, size)
ans = min(ans, res)
if(ans == INF): print(-1)
else: print(ans)