#include <iostream>
#include <map>
#include <queue>
#include <cmath>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
using namespace std;
#pragma warning (disable: 4996)

long long solve(vector<int> vec) {
	long long minx = (1LL << 60), ret = (1LL << 60);
	for (int i = (int)vec.size() - 1; i >= 0; i--) {
		if (vec[i] > minx) ret = min(ret, 1LL * vec[i] + minx);
		minx = min(minx, 1LL * vec[i]);
	}
	return ret;
}

long long N, A[1 << 18];

int main() {
	cin >> N;
	for (int i = 1; i <= N; i++) cin >> A[i];

	pair<long long, int> minx = make_pair(1LL << 60, -1);
	for (int i = 1; i <= N; i++) minx = min(minx, make_pair(A[i], i));

	// パターン 1
	long long cl = (1LL << 60), cr = (1LL << 60);
	for (int i = 1; i <= minx.second - 1; i++) cl = min(cl, A[i]);
	for (int i = minx.second + 1; i <= N; i++) cr = min(cr, A[i]);
	long long z1 = cl + cr + A[minx.second];

	// パターン 2
	vector<int> val;
	for (int i = minx.second + 1; i <= N; i++) val.push_back(A[i]);
	long long z2 = solve(val) + A[minx.second];

	// パターン 3
	vector<int> val2;
	for (int i = minx.second - 1; i >= 1; i--) val2.push_back(A[i]);
	long long z3 = solve(val2) + A[minx.second];

	if (min({ z1, z2, z3 }) >= (1LL << 60)) cout << "-1" << endl;
	else cout << min({ z1, z2, z3 }) << endl;
	return 0;
}