#include <bits/stdc++.h>
#define rep(i, a, n) for (int i = a; i < n; i++)
#define repr(i, a, n) for (int i = n - 1; i >= a; i--)
using namespace std;
using ll = long long;
using P = pair<int, int>;
template <typename T> void chmin(T &a, T b) { a = min(a, b); }
template <typename T> void chmax(T &a, T b) { a = max(a, b); }

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);

  int n;
  cin >> n;
  vector<int> a(n);
  rep(i, 0, n) cin >> a[i];

  vector<int> min_l(n + 1, 1e9), min_r(n + 1, 1e9);
  rep(i, 0, n) { min_l[i + 1] = min(min_l[i], a[i]); }
  repr(i, 0, n) { min_r[i] = min(min_r[i + 1], a[i]); }

  int ans = 1e9;

  rep(i, 1, n - 1) {
    if (min_l[i] > a[i] || min_r[i + 1] > a[i])
      continue;
    chmin(ans, a[i] + min_l[i] + min_r[i + 1]);
  }

  vector<int> max_l(n+1,1e9), max_r(n+1,1e9);
  set<int> st1, st2;
  rep(i,0,n-1){
    auto it = st1.upper_bound(a[i]);
    if (it != st1.end())max_l[i]=*it;
    st1.insert(a[i]);
  }

  repr(i,1,n){
    auto it = st2.upper_bound(a[i]);
    if (it !=st2.end()) max_r[i+1]=*it;
    st2.insert(a[i]);
  }

  int ans2 = 1e9;
  rep(i,1,n){
    chmin(ans2, a[i] + max_l[i] + max_r[i + 1]);
  }

  chmin(ans, ans2);
  if (ans == 1e9)
    cout << -1 << endl;
  else
    cout << ans << endl;
}