#include <iostream>
#include<vector>
#include<algorithm>
#include<string>
#include<map>
#include<set>
#include<stack>
#include<queue>
#include<math.h>
using namespace std;
typedef long long ll;
#define int long long
#define double long double
typedef vector<int> VI;
typedef pair<int, int> pii;
typedef vector<pii> VP;
typedef vector<string> VS;
typedef priority_queue<int> PQ;
template<class T>bool chmax(T &a, const T &b) { if (a < b) { a = b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b < a) { a = b; return 1; } return 0; }
#define fore(i,a) for(auto &i:a)
#define REP(i,n) for(int i=0;i<n;i++)
#define eREP(i,n) for(int i=0;i<=n;i++)
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define eFOR(i,a,b) for(int i=(a);i<=(b);++i)
#define SORT(c) sort((c).begin(),(c).end())
#define rSORT(c) sort((c).rbegin(),(c).rend())
#define LB(x,a) lower_bound((x).begin(),(x).end(),(a))
#define UB(x,a) upper_bound((x).begin(),(x).end(),(a))
#define INF 1000000000
#define LLINF 9223372036854775807
#define mod 1000000007
#define eps 1e-12 
//priority_queue<int,vector<int>, greater<int> > q2;



signed main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

	int N; cin >> N;
	VI A(N);
	set<int>S1, S2;
	REP(i, N) {
		cin >> A[i];
		if (i > 1)S2.insert(A[i]);
	}
	S1.insert(A[0]);
	int ans = INF;
	
	VI mi1(N, INF), mi2(N, INF);
	mi1[0] = A[0];
	mi2[N - 1] = A[N - 1];
	FOR(i, 1, N)mi1[i] = min(mi1[i - 1], A[i]);
	for (int i = N - 2; i >= 0; i--)mi2[i] = min(mi2[i + 1], A[i]);
	FOR(i, 1, N - 1) {
		if (mi1[i - 1] < A[i] && mi2[i + 1] < A[i]) {
			chmin(ans, A[i] + mi1[i - 1] + mi2[i + 1]);
		}

		auto it1 = S1.lower_bound(A[i]);
		auto it2 = S2.lower_bound(A[i]);
		if (it1 != S1.end() && it2 != S2.end()) {
			chmin(ans, *it1 + *it2 + A[i]);
		}
		S2.erase(S2.find(A[i + 1]));
		S1.insert(A[i]);

	}
	if (ans == INF)ans = -1;
	cout << ans << endl;

	return 0;
}