import sys
input=lambda: sys.stdin.readline().rstrip()
n=int(input())
A=[int(i) for i in input().split()]
ans=float("inf")
L=[A[0]]
for i in range(1,n):
  L.append(min(L[-1],A[i]))
R=[A[-1]]
for i in range(n-1)[::-1]:
  R.append(min(R[-1],A[i]))
R=R[::-1]

for i in range(1,n-1):
  if L[i-1]<A[i] and R[i+1]<A[i]:
    ans=min(ans,L[i-1]+A[i]+R[i+1])

k=A.index(min(A))
if k==0 or k==n-1:
  if ans==float("inf"):
    print(-1)
  else:
    print(ans)
else:
  l,r=min(A[:k]),min(A[k+1:])
  ans=min(ans,l+r+A[k])
  print(ans)