#include "bits/stdc++.h"
using namespace std;
#define int long long
#define REP(i, n) for (int i = 0; i < (int)n; ++i)
#define RREP(i, n) for (int i = (int)n - 1; i >= 0; --i)
#define FOR(i, s, n) for (int i = s; i < (int)n; ++i)
#define RFOR(i, s, n) for (int i = (int)n - 1; i >= s; --i)
#define ALL(a) a.begin(), a.end()
#define IN(a, x, b) (a <= x && x < b)
template<class T>inline void out(T t){cout << t << "\n";}
template<class T,class... Ts>inline void out(T t,Ts... ts){cout << t << " ";out(ts...);}
template<class T>inline bool CHMIN(T&a,T b){if(a > b){a = b;return true;}return false;}
template<class T>inline bool CHMAX(T&a,T b){if(a < b){a = b;return true;}return false;}
constexpr int INF = 1e18;



signed main(){
	int N;
	cin >> N;
	vector<int>a(N);
	multiset<int>l,r;
	REP(i,N){
		cin >> a[i];
		r.insert(a[i]);
	}
	int ans = INF;
	REP(i,N){
		r.erase(r.find(a[i]));

		if(l.size() && r.size()){
			int lmi = *l.begin();
			int rmi = *r.begin();
			if(a[i] > lmi && a[i] > rmi){
				CHMIN(ans,a[i]+lmi+rmi);
			}
		}
		if(l.upper_bound(a[i]) != l.end() && r.upper_bound(a[i]) != r.end()){
			int lup = *l.upper_bound(a[i]);
			int rup = *r.upper_bound(a[i]);
			CHMIN(ans,a[i]+lup+rup);
		}

		l.insert(a[i]);
	}
	out((ans == INF) ? -1 : ans);
}