#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);

	std::vector<LLONG> ai(N), minL(N + 1, MOD_NUM), minR(N + 1, MOD_NUM);
	LLONG minVal = MOD_NUM;
	std::set<LLONG> left, right;
	for (int i = 0; i < N; i++) {
		getval(ai[i]);

		minL[i + 1] = minL[i];
		if (minVal > ai[i]) {
			minVal = ai[i];
			minL[i + 1] = minVal;
		}
		right.insert(ai[i]);
	}

	minVal = MOD_NUM;
	for (int i = N - 1; i > 0; i--) {
		minR[i] = minR[i + 1];
		if (minVal > ai[i]) {
			minVal = ai[i];
			minR[i] = minVal;
		}
	}

	LLONG ans = MOD_NUM, pta = 0, ptb = 0;
	left.insert(ai[0]);
	right.erase(ai[0]);
	for (int i = 1; i < N - 1; i++) {
		if ((minL[i] < ai[i]) && (ai[i] > minR[i])) {
			pta = minL[i] + ai[i] + minR[i];
			if (ans > pta) {
				ans = pta;
			}
		}

		right.erase(ai[i]);
		auto lm = left.lower_bound(ai[i]);
		auto rm = right.lower_bound(ai[i]);
		if (lm != left.end() && rm != right.end()) {
			ptb = *lm + ai[i] + *rm;
			if (ans > ptb) {
				ans = ptb;
			}
		}
		left.insert(ai[i]);
	}

	if (ans >= MOD_NUM) ans = -1;
	printf("%lld\n", ans);
}