#pragma GCC optimize ("O2")
#pragma GCC target ("avx2")
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i, n) for(int i = 0; i < (n); i++)
#define rep1(i, n) for(int i = 1; i <= (n); i++)
#define co(x) cout << (x) << "\n"
#define cosp(x) cout << (x) << " "
#define ce(x) cerr << (x) << "\n"
#define cesp(x) cerr << (x) << " "
#define pb push_back
#define mp make_pair
#define chmin(x, y) x = min(x, y)
#define chmax(x, y) x = max(x, y)
#define Would
#define you
#define please


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


	int N;
	cin >> N;

	int A[200200];
	rep(i, N) cin >> A[i];

	int L[200200], R[200200];
	int saishou = 1e9;
	rep(i, N) {
		chmin(saishou, A[i]);
		L[i] = saishou;
	}
	saishou = 1e9;
	for (int i = N - 1; i >= 0; i--) {
		chmin(saishou, A[i]);
		R[i] = saishou;
	}
	int kotae = 1e9;
	rep1(i, N - 2) {
		if (A[i] > L[i] && A[i] > R[i]) {
			chmin(kotae, L[i] + A[i] + R[i]);
		}
	}
	int saidai = 0;
	rep(i, N) {
		chmax(saidai, A[i]);
		L[i] = saidai;
	}
	saidai = 0;
	for (int i = N - 1; i >= 0; i--) {
		chmax(saidai, A[i]);
		R[i] = saidai;
	}
	rep1(i, N - 2) {
		if (A[i] < L[i] && A[i] < R[i]) {
			chmin(kotae, L[i] + A[i] + R[i]);
		}
	}

	if (kotae > 5e8) {
		co(-1);
	}
	else co(kotae);

	Would you please return 0;
}