#include<bits/stdc++.h>
using namespace std;

#define int long long
#define ll long long
#define pb push_back
#define mp make_pair
#define f(i,a,n) for(int i=a ; i<n ; i++)
#define rf(i,n,a) for(int i=n ; i>=a ; i--)
#define F first
#define S second
#define all(c) (c).begin(),(c).end()
#define sz(v) (int)(v).size()
#define fast ios::sync_with_stdio(0); cin.tie(0); cout.tie(0)

typedef long double ld;
typedef vector<int> vi;
typedef pair<int,int> pii;
typedef pair<pii,int> ppi;
typedef vector<pii> vpi;

const int inf = 1e9;
const int inf64 = 1e18;
const int MOD = inf + 7;

int get(int a , int b , int c){
   if(b > a && b > c){
      return a + b + c;
   }
   if(b < a && b < c){
      return a + b + c;
   }
   return inf64;
}

void solve(){
   int n;
   cin >> n;

   int a[n];
   f(i,0,n) cin >> a[i];

   vi ps(n) , pb(n) , ss(n) , sb(n);

   ps[0] = a[0];
   pb[0] = a[0];

   f(i,1,n){
      ps[i] = min(ps[i-1] , a[i]);
      pb[i] = max(pb[i-1] , a[i]);
   }

   ss[n-1] = a[n-1];
   sb[n-1] = a[n-1];

   rf(i,n-2,0){
      ss[i] = min(ss[i+1] , a[i]);
      sb[i] = max(sb[i+1] , a[i]);
   }

   int ans = inf64;

   f(i,1,n-1){
      ans = min(ans , get(ps[i-1] , a[i] , ss[i+1]));
      ans = min(ans , get(ps[i-1] , a[i] , sb[i+1]));
      ans = min(ans , get(pb[i-1] , a[i] , ss[i+1]));
      ans = min(ans , get(pb[i-1] , a[i] , sb[i+1]));
   }

   if(ans  > inf) ans = -1;
   cout << ans << "\n";
}

int32_t main(){
   fast;
   int t = 1;
   // cin >> t;
   while(t--)  solve();   
}