N=int(input())
A=list(map(int, input().split()))
LMI=[0 for i in range(N)]
RMI=[0 for i in range(N)]
mi,ma=10**9,0
for i in range(N):
    mi=min(A[i],mi)
    LMI[i]=mi
    
mi,ma=10**9,0
for i in range(N):
    mi=min(A[-1-i],mi)
    RMI[-1-i]=mi
ans=10**9
for i in range(1,N-1):
    if LMI[i-1]<A[i] and A[i]>RMI[i+1]:
        d=LMI[i-1]+A[i]+RMI[i+1]
        ans=min(d,ans)
import bisect
import heapq
L=[]
R=sorted(A)
R.remove(A[0])
for i in range(1,N-1):
    heapq.heappush(L,A[i-1]) 
    R.remove(A[i])
    a=bisect.bisect_right(L,A[i])
    b=bisect.bisect_right(R,A[i])
    if a!=i and b!=N-i-1:
        d=L[a]+A[i]+R[b]
        ans=min(d,ans)
if ans==10**9:
    print(-1)
else:
    print(ans)