#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <string>
#include <map>
#include <set>
#include <stack>
#include <tuple>
#include <deque>
#include <array>
#include <numeric>
#include <bitset>
#include <iomanip>
#include <cassert>
#include <chrono>
#include <random>
#include <limits>
#include <iterator>
#include <functional>
#include <sstream>
#include <fstream>
#include <complex>
#include <cstring>
#include <unordered_map>
#include <unordered_set>
using namespace std;

using ll = long long;
using P = pair<int, int>;
constexpr int INF = 1001001001;
// constexpr int mod = 1000000007;
constexpr int mod = 998244353;

template<class T>
inline bool chmax(T& x, T y){
    if(x < y){
        x = y;
        return true;
    }
    return false;
}
template<class T>
inline bool chmin(T& x, T y){
    if(x > y){
        x = y;
        return true;
    }
    return false;
}

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

    int n;
    cin >> n;
    vector<int> a(n);
    for(int i = 0; i < n; ++i)  cin >> a[i];

    map<int, int> mp, mp2;
    mp[a[0]] = 1;
    for(int i = 2; i < n; ++i)  mp2[a[i]] += 1;
    int ans = INF;
    for(int i = 1; i < n - 1; ++i){
        int l = mp.begin()->first, r = mp2.begin()->first;
        if(a[i] <= l || a[i] <= r)  continue;
        if(l != r)  chmin(ans, l + a[i] + r);
        else{
            auto it = mp.begin();
            it++;
            if(it != mp.end() && it->first < a[i]){
                chmin(ans, it->first + a[i] + r);
            }
            it = mp2.begin();
            it++;
            if(it != mp2.end() && it->first < a[i]){
                chmin(ans, l + a[i] + it->first);
            }
        }
        mp[a[i]] += 1;
        if(--mp2[a[i + 1]] == 0)    mp2.erase(a[i + 1]);
    }

    mp.clear(); mp2.clear();
    mp[-a[0]] = 1;
    for(int i = 2; i < n; ++i)  mp2[-a[i]] += 1;
    for(int i = 1; i < n - 1; ++i){
        int l = -mp.begin()->first, r = -mp2.begin()->first;
        if(a[i] >= l || a[i] >= r)  continue;
        if(l != r)  chmin(ans, l + a[i] + r);
        else{
            auto it = mp.begin();
            it++;
            if(it != mp.end() && -it->first > a[i]){
                chmin(ans, -it->first + a[i] + r);
            }
            it = mp2.begin();
            it++;
            if(it != mp2.end() && -it->first > a[i]){
                chmin(ans, l + a[i] - it->first);
            }
        }
        mp[-a[i]] += 1;
        if(--mp2[-a[i + 1]] == 0)   mp2.erase(-a[i + 1]);
    }

    if(ans == INF)  ans = -1;
    cout << ans << endl;

    return 0;
}