#include <iostream>
#include <string>
#include <vector>
#include <queue>
#include <deque>
#include <algorithm>
#include <set>
#include <map>
#include <bitset>
#include <cmath>
#include <functional>
#include <iomanip>
#define vll vector<ll>
#define vvvl vector<vvl>
#define vvl vector<vector<ll>>
#define VV(a, b, c, d) vector<vector<d>>(a, vector<d>(b, c))
#define VVV(a, b, c, d) vector<vvl>(a, vvl(b, vll (c, d)));
#define re(c, b) for(ll c=0;c<b;c++)
#define rep(a,b,c) for(ll a=b;a<c;a++)
#define all(obj) (obj).begin(), (obj).end()
typedef long long int ll;
typedef long double ld;
using namespace std;

void get(vll &a){re(i,a.size()) scanf("%lld",&a[i]);}
void get(vvl &a){re(i,a.size()) re(j,a[0].size()) scanf("%lld",&a[i][j]);}
void print(vll &a){re(i,a.size()) cout<<a[i]<<(i==a.size()-1?"\n":" ");}
void print(vvl &a){re(i,a.size()) re(j,a[0].size())cout<<a[i][j]<<(j==a[0].size()-1?"\n":" ");}

int main(int argc, char const *argv[]) {
  ll n;std::cin >> n;
  vll a(n);get(a);
  set<ll> l, r;
  vll min_l(n, -1), max_l(n, -1);
  vll min_r(n, -1), max_r(n, -1);


  for(int i=0;i<n;i++){
    auto itr = l.upper_bound(a[i]);
    if(itr!=l.end()) max_l[i] = (*itr);
    if(itr!=l.begin()) min_l[i] = (*l.begin());
    l.insert(a[i]);
  }
  for(int i=n-1;i>=0;i--){
    auto itr = r.upper_bound(a[i]);
    if(itr!=r.end()) max_r[i] = (*itr);
    if(itr!=r.begin()) min_r[i] = (*r.begin());
    r.insert(a[i]);
  }
  ll ans = 1000000000000;
  re(i, n){
    //if(a[i]==39) std::cout << min_l[i] << " " << min_r[i] << '\n';
    if(min_l[i]!=-1&&min_r[i]!=-1) ans = min(ans, min_l[i]+min_r[i]+a[i]);
    if(max_l[i]!=-1&&max_r[i]!=-1) ans = min(ans, max_l[i]+max_r[i]+a[i]);
  }
  std::cout << (ans==1000000000000?-1:ans) << '\n';
}