#include <bits/stdc++.h>
using namespace std;
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) begin(v),end(v)
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
using ll = long long;
using pii = pair<int, int>;
constexpr ll INF = 1ll<<30;
constexpr ll longINF = 1ll<<60;
constexpr ll MOD = 1000000007;
constexpr bool debug = false;
//---------------------------------//

int main() {
	int N;
	cin >> N;
	vector<int> A(N);
	REP(i, N) scanf("%d", &A[i]);
	
	int ans = INF;
	set<int> front, back;
	FOR(i, 2, N) back.insert(A[i]);
	FOR(i, 1, N - 1) {
		front.insert(A[i - 1]);
		
		auto it1 = front.lower_bound(A[i]);
		auto it2 = back.lower_bound(A[i]);
		if (it1 != front.end() && it2 != back.end()) chmin(ans, A[i] + *it1 + *it2);
		
		if (*front.begin() < A[i] && *back.begin() < A[i]) chmin(ans, A[i] + *front.begin() + *back.begin());
		back.erase(A[i + 1]);
	}
	if (ans == INF) puts("-1");
	else cout << ans << endl;
}