/**
 *    author:  otera    
**/
#include<iostream>
#include<string> 
#include<cstdio>
#include<cstring>
#include<vector>
#include<cmath>
#include<algorithm> 
#include<functional>
#include<iomanip>
#include<queue>
#include<deque>
#include<ciso646>
#include<random>
#include<map>
#include<set>
#include<complex>
#include<bitset>
#include<stack>
#include<unordered_map>
#include<utility>
#include<cassert>
using namespace std;

#define int long long
typedef long long ll;
typedef unsigned long long ul;
typedef unsigned int ui;
typedef long double ld;
const int inf=1e9+7;
const ll INF=1LL<<60 ;
const ll mod=1e9+7 ;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define Rep(i,sta,n) for(int i=sta;i<n;i++)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define per1(i,n) for(int i=n;i>=1;i--)
#define Rep1(i,sta,n) for(int i=sta;i<=n;i++)
typedef complex<ld> Point;
const ld eps = 1e-8;
const ld pi = acos(-1.0);
typedef pair<int, int> P;
typedef pair<ld, ld> LDP;
typedef pair<ll, ll> LP;
#define fr first
#define sc second
#define all(c) c.begin(),c.end()
#define pb push_back
#define debug(x)  cerr << #x << " = " << (x) << endl;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

void solve() {
	int n; cin >> n;
    vector<int> a(n);
    rep(i, n) {
        cin >> a[i];
    }
    multiset<int> left, right;
    for(int i = 2; i < n; ++ i) {
        right.insert(a[i]);
    }
    left.insert(a[0]);
    int ans = INF;
    for(int i = 1; i < n - 1; ++ i) {
        int b = a[i];
        int lmi = *left.begin(), lma = *left.upper_bound(b);
        int rmi = *right.begin(), rma = *right.upper_bound(b);
        if(lmi < b && rmi < b) {
            //cerr << b << endl;
            chmin(ans, lmi + b + rmi);
        }
        if(lma > b && rma > b) {
            //cerr << lma + b + rma << endl;
            chmin(ans, lma + b + rma);
        }
        left.insert(b);
        right.erase(a[i + 1]);
    }
    if(ans == INF) {
        cout << -1 << endl;
    } else {
        cout << ans << endl;
    }
}

signed main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	//cout << fixed << setprecision(10);
	//int t; cin >> t; rep(i, t)solve();
	solve();
    return 0;
}