#include <stdio.h>
#include <string.h>
#include <limits.h>
#include <math.h>
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <map>
#include <set>
#include <stack>
#include <queue>

typedef unsigned long long ULLONG;
typedef long long LLONG;
static const LLONG MOD_NUM = 1000000007;//998244353;

template<class _T> static void getval(_T& a) {
	std::cin >> a;
}
template<class _T> static void getval(_T& a, _T& b) {
	std::cin >> a >> b;
}
template<class _T> static void getval(_T& a, _T& b, _T& c) {
	std::cin >> a >> b >> c;
}

static void exec();

int main()
{
	exec();
	fflush(stdout);
	return 0;
}

static void exec()
{
	int N;
	getval(N);

	int INF = MOD_NUM * 2LL;
	LLONG minVal = INF;
	int minIdx = -1;
	std::vector<LLONG> ai(N);
	for (int i = 0; i < N; i++) {
		getval(ai[i]);

		if (minVal > ai[i]) {
			minVal = ai[i];
			minIdx = i;
		}
	}

	LLONG ans = 0;
	LLONG fMin = INF, fPeak = INF, fFst = INF;
	std::set<LLONG> fs;
	for (int i = minIdx - 1; i >= 0; i--) {
		if (fMin > ai[i]) {
			fMin = ai[i];
		}
		if (fFst > ai[i]) {
			auto f = fs.lower_bound(ai[i]);
			if (f != fs.end()) {
				fFst = ai[i];
				fPeak = *f;
			}
		}
		fs.insert(ai[i]);
	}

	fs.erase(fs.begin(), fs.end());
	LLONG lMin = INF, lPeak = INF, lLast = INF;
	for (int i = minIdx + 1; i < N; i++) {
		if (lMin > ai[i]) {
			lMin = ai[i];
		}

		if (lLast > ai[i]) {
			auto l = fs.lower_bound(ai[i]);
			if (l != fs.end()) {
				lLast = ai[i];
				lPeak = *l;
			}
		}
		fs.insert(ai[i]);
	}
	ans = std::min({ fMin + minVal + lMin, fFst + fPeak + minVal, minVal + lPeak + lLast });
	if (ans > INF) ans = -1;
	printf("%lld\n", ans);
}