#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];

    set<int> prefix, suffix;
    prefix.emplace(a[0]);
    for(int i = 2; i < n; ++i)  suffix.emplace(a[i]);

    int ans = INF;
    for(int i = 1; i < n - 1; ++i){
        auto left = prefix.begin(), right = suffix.begin();
        if(*left < a[i] && a[i] > *right) chmin(ans, *left + a[i] + *right);
        
        left = prefix.upper_bound(a[i]), right = suffix.lower_bound(a[i]);
        if(left != prefix.end() && right != suffix.end()){
            chmin(ans, *left + a[i] + *right);
        }

        prefix.emplace(a[i]);
        suffix.erase(a[i + 1]);
    }

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

    return 0;
}