#include <iostream>
#include <cstdio>
#include <cmath>
#include <ctime>
#include <cstdlib>
#include <cassert>
#include <vector>
#include <list>
#include <stack>
#include <queue>
#include <deque>
#include <map>
#include <set>
#include <bitset>
#include <string>
#include <algorithm>
#include <utility>
#define llint long long
#define inf 1e18
#define rep(x, s, t) for(llint (x) = (s); (x) < (t); (x)++)
#define Rep(x, s, t) for(llint (x) = (s); (x) <= (t); (x)++)
#define chmin(x, y) (x) = min((x), (y))
#define chmax(x, y) (x) = max((x), (y))

using namespace std;
typedef pair<llint, llint> P;

llint n;
llint a[200005];
set<llint> S;
llint l[200005], l2[200005];
llint r[200005], r2[200005];

int main(void)
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	cin >> n;
	for(int i = 1; i <= n; i++){
		cin >> a[i];
		l[i] = l2[i] = r[i] = r2[i] = inf;
	}
	
	for(int i = 1; i <= n; i++){
		if(S.size()) l[i] = *S.begin();
		auto it = S.upper_bound(a[i]);
		if(it != S.end()) l2[i] = *it;
		S.insert(a[i]);
	}
	
	S.clear();
	for(int i = n; i >= 1; i--){
		if(S.size()) r[i] = *S.begin();
		auto it = S.upper_bound(a[i]);
		if(it != S.end()) r2[i] = *it;
		S.insert(a[i]);
	}
	
	llint ans = inf;
	for(int i = 1; i <= n; i++){
		if(l[i] < a[i] && r[i] < a[i]) ans = min(ans, l[i]+a[i]+r[i]);
		ans = min(ans, l2[i]+a[i]+r2[i]);
	}
	if(ans > inf/2) ans = -1;
	
	cout << ans << endl;
	
	return 0;
}