#include <cstdio>
#include <iostream>
#include <string>
#include <sstream>
#include <stack>
#include <algorithm>
#include <cmath>
#include <queue>
#include <map>
#include <set>
#include <cstdlib>
#include <bitset>
#include <tuple>
#include <assert.h>
#include <deque>
#include <bitset>
#include <iomanip>
#include <limits>
#include <chrono>
#include <random>
#include <array>
#include <unordered_map>
#include <functional>
#include <complex>
#include <numeric>
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; }
constexpr long long MAX = 5100000;
constexpr long long INF = 1LL << 60;
constexpr int inf = 1000000007;
constexpr long long mod = 1000000007LL;
//constexpr long long mod = 998244353LL;
const long double PI = acos((long double)(-1));

using namespace std;
typedef unsigned long long ull;
typedef long long ll;
typedef long double ld;

int main()
{
	/*
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	*/

	int n; scanf("%d", &n);
	vector<ll> a(n); for (int i = 0; i < n; i++) scanf("%lld", &a[i]);
	set<ll> lf, rg;
	for (int i = 1; i < n; i++) rg.emplace(a[i]);
	lf.emplace(a[0]);
	lf.emplace(INF);
	rg.emplace(INF);
	ll res = inf;
	for (int i = 1; i < n - 1; i++) {
		rg.erase(rg.find(a[i]));
		{
			ll mnl = *lf.begin();
			ll mnr = *rg.begin();
			if (mnl < a[i] and a[i] > mnr) chmin(res, a[i] + mnl + mnr);
		}
		{
			ll mnl = *lf.lower_bound(a[i]);
			ll mnr = *rg.lower_bound(a[i]);
			chmin(res, a[i] + mnl + mnr);
		}
		lf.emplace(a[i]);
	}
	if (res >= inf) res = -1;
	cout << res << endl;
	return 0;
}