import sys
input = sys.stdin.readline
from bisect import bisect_left, bisect_right

# example()

N=int(input())
A=list(map(int, input().split()))


INF=float("inf")
left_u=[-1]*N
left_d=[INF]*N

u,d=-1,INF

for i in range(N):
    if u>A[i]:
        left_u[i]=u
    if d<A[i]:
        left_d[i]=d
    u=max(u,A[i])
    d=min(d,A[i])

right_u=[-1]*N
right_d=[INF]*N

u,d=-1,INF

for i in range(N)[::-1]:
    if u>A[i]:
        right_u[i]=u
    if d<A[i]:
        right_d[i]=d
    u=max(u,A[i])
    d=min(d,A[i])

res=INF
for i in range(1,N-1):
    if left_u[i]!=-1 and right_u[i]!=-1:
        res=min(A[i]+left_u[i]+right_u[i],res)
    if left_d[i]!=INF and right_d[i]!=INF:
        res=min(A[i]+left_d[i]+right_d[i],res)
    # print(i,A[i],left_u[i],right_u[i])


print(res if res!=INF else -1)