#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <string>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <iomanip>
#include <utility>
#include <tuple>
#include <functional>
#include <bitset>
#include <cassert>
#include <complex>
#include <stdio.h>
#include <time.h>
#include <numeric>
#include <random>
#include <unordered_map>
#include <unordered_set>
#define all(a) a.begin(),a.end()
#define rep(i, n) for (ll i = 0; i < (n); i++)
#define pb push_back
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<ll, ll> P;
typedef complex<ld> com;
constexpr int inf = 1000000010;
constexpr ll INF = 1000000000000000010;
constexpr ld eps = 1e-12;
constexpr ld pi = 3.141592653589793238;
template<class T, class U> inline bool chmax(T &a, const U &b) { if (a < b) { a = b; return true; } return false; }
template<class T, class U> inline bool chmin(T &a, const U &b) { if (a > b) { a = b; return true; } return false; }


signed main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	cout << fixed << setprecision(20);

	int n;
	cin >> n;
	vector<int> a(n);
	rep(i, n) cin >> a[i];
	int ans = inf;
	set<int> left, right;
	left.insert(inf); right.insert(inf);
	for (int i = 1; i < n; i++) right.insert(a[i]);
	rep(i, n) {
		auto itr = right.lower_bound(a[i]);
		auto itl = left.lower_bound(a[i]);
		if (*itr != inf && *itl != inf) chmin(ans, *itr + *itl + a[i]);
		itr = left.begin(); itl = right.begin();
		if (*itr < a[i] && *itl < a[i]) chmin(ans, *itr + *itl + a[i]);
		left.insert(a[i]);
		if (i != n - 1) right.erase(a[i + 1]);
	}
	if (ans == inf) cout << "-1\n";
	else cout << ans << '\n';
}