#pragma region
#define _USE_MATH_DEFINES
#include <iostream>
#include <string>
#include <algorithm>
#include <cmath>
#include <cstdlib>
#include <vector>
#include <map>
#include <queue>
#include <stack>
#include <set>
#include <list>
#include <iomanip>
#include <cstdint>
#include <bitset>
#include <sstream>
#include <regex>
#include <fstream>
#include <array>
#include <atcoder/all>

using namespace atcoder;
using mint = modint1000000007;
//using mint = modint998244353;
//using mint = modint;
using namespace std;
typedef long long ll;
using vi = vector<int>;
using vvi = vector<vi>;
using vl = vector<ll>;
using vvl = vector<vl>;
using pint = pair<int, int>;
using pll = pair<ll, ll>;
using vpint = vector<pint>;
using vvpint = vector<vpint>;
using vmint = vector<mint>;
using vvmint = vector<vmint>;
//#define rep(i, s, e) for (int(i) = (s); (i) < (e); ++(i))
#define rep(i, e) for (int(i) = 0; (i) < (e); ++(i))
#define rrep(i, s) for (int(i) = (s) - 1; (i) >= 0; --(i))
#define all(x) x.begin(),x.end()
#define rall(x) x.rbegin(),x.rend()

#pragma region GCD
ll gcd(ll a, ll b)
{
	if (b == 0)return a;
	return gcd(b, a % b);
}
#pragma endregion
#pragma region LCM
ll lcm(ll a, ll b)
{
	return a / gcd(a, b) * b;
}
#pragma endregion
#pragma region chmin
template<class T> inline bool chmin(T& a, T b)
{
	if (a > b)
	{
		a = b;
		return true;
	}
	return false;
}
#pragma endregion
#pragma region chmax
template<class T> inline bool chmax(T& a, T b)
{
	if (a < b)
	{
		a = b;
		return true;
	}
	return false;
}
#pragma endregion
#pragma region グリッド内チェック
bool out(int x, int y, int h, int w)
{
	if (x < 0 || h <= x || y < 0 || w <= y)return true;
	else return false;
}
#pragma endregion
#pragma region Dijkstra
vl dijkstra(vector<vector<pair<int, ll>>> v, int s)
{
	ll INF = 1e18;
	int MAX = 1e6;
	vl res(MAX, INF);
	priority_queue<pair<ll, int>, vector<pair<ll, int>>, greater<pair<ll, int>>> q;
	q.push({ 0,s });
	while (!q.empty())
	{
		int now;
		ll d;
		tie(d, now) = q.top();
		q.pop();
		if (!chmin(res[now], d))continue;
		for (auto p : v[now])
		{
			int next;
			ll c;
			tie(next, c) = p;
			if (res[next] <= res[now] + c)continue;
			q.push({ res[now] + c,next });
		}
	}
	return res;
}
#pragma endregion
#pragma endregion


int main()
{
	int n; cin >> n;
	vi a(n); rep(i, n)cin >> a[i];
	vi lsmall(n), rsmall(n);
	lsmall[0] = a[0];
	rsmall[n - 1] = a[n - 1];
	for (int i = 1; i < n; ++i)lsmall[i] = min(lsmall[i - 1], a[i]);
	rrep(i, n - 1)rsmall[i] = min(rsmall[i + 1], a[i]);
	int res = 1e9;
	for (int i = 1; i < n - 1; ++i)
	{
		if (a[i] > lsmall[i - 1] && a[i] > rsmall[i + 1])
		{
			chmin(res, a[i] + lsmall[i - 1] + rsmall[i + 1]);
		}
	}
	set<int> l, r;
	l.insert(a[0]);
	rep(i, n - 1)r.insert(a[i + 1]);
	for (int i = 1; i < n - 1; ++i)
	{
		r.erase(a[i]);
		auto lit = l.lower_bound(a[i]);
		auto rit = r.lower_bound(a[i]);
		if (lit == l.end() || rit == r.end())continue;
		chmin(res, *lit + a[i] + *rit);
	}
	if (res == 1e9)cout << -1 << endl;
	else cout << res << endl;
}