#!/usr/bin/env python3

import sys
input=sys.stdin.readline

n=int(input())
arr=list(map(int,input().split()))
left_min=[10**18]
for i in range(n):
    left_min.append(min(left_min[-1],arr[i]))
right_min=[10**18]
for i in range(n-1,-1,-1):
    right_min.append(min(right_min[-1],arr[i]))
right_min=right_min[::-1]
ans=10**18
for i in range(1,n-1):
    a,b,c=left_min[i],arr[i],right_min[i+1]
    if (b<a and b<c) or (b>a and b>c):
        ans=min(ans,a+b+c)
if ans==10**18:
    print(-1)
else:
    print(ans)