from sortedcontainers import SortedList
N = int(input())
A = list(map(int,input().split()))
INFTY = 10**14
Bl = [0]*N
Br = [0]*N
Cl = [0]*N
Cr = [0]*N
L = SortedList()
L.add(A[0])
for i in range(N):
    if A[i]>L[0]:
        Bl[i] = L[0]
    else:
        Bl[i] = INFTY
    if L.bisect_right(A[i])<len(L):
        Cl[i] = L[L.bisect_right(A[i])]
    else:
        Cl[i] = INFTY
    L.add(A[i])
R = SortedList()
R.add(A[N-1])
for i in range(N-1,-1,-1):
    if A[i]>R[0]:
        Br[i] = R[0]
    else:
        Br[i] = INFTY
    if R.bisect_right(A[i])<len(R):
        Cr[i] = R[R.bisect_right(A[i])]
    else:
        Cr[i] = INFTY
    R.add(A[i])
ans = INFTY
for i in range(N):
    ans = min(ans,A[i]+Bl[i]+Br[i],A[i]+Cl[i]+Cr[i])
if ans>=INFTY:
    print(-1)
else:
    print(ans)