#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define REP(i,m,n) for(int i=(int)(m); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define RREP(i,m,n) for(int i=(int)(m); i>=(int)(n); i--)
#define rrep(i,n) RREP(i,n-1,0)
#define all(v) v.begin(), v.end()
const int inf = 1e9+7;
const ll longinf = 1LL<<60;
const ll mod = 1e9+7;

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  int N; cin >> N;
  vector<ll> A(N); rep(i, N) cin >> A[i];
  map<ll, int> mpl, mpr;
  rep(i, N) mpr[A[i]]++;
  ll mn = longinf;
  rep(i, N) {
    mpr[A[i]]--;
    if(mpr[A[i]]==0) mpr.erase(A[i]);
    if(!mpl.empty() && !mpr.empty()) {
      auto itrl = mpl.begin(), itrr = mpr.begin();
      while(itrl != mpl.end() && itrl->first == A[i]) itrl++;
      while(itrr != mpl.end() && itrr->first == A[i]) itrr++;
      if(itrl != mpl.end() && itrr != mpr.end()) {
        if(itrl->first > A[i] || itrr->first > A[i]) continue;
        if(itrl->first == itrr->first) {
          auto tmp = itrl;
          while(tmp != mpl.end() && tmp->first == A[i]) tmp++;
          if(tmp != mpl.end() && tmp->first < A[i]) {
            mn = min(A[i]+tmp->first+itrr->first, mn);
          }
          tmp = itrr;
          while(tmp != mpr.end() && tmp->first == A[i]) tmp++;
          if(tmp != mpr.end() && tmp->first < A[i]) {
            mn = min(A[i]+itrl->first+tmp->first, mn);
          }
        } else {
          mn = min(A[i]+itrl->first+itrr->first, mn);
        }
      }
    }
    mpl[A[i]]++;
  }
  cout << (mn == longinf ? -1 : mn) << "\n";
  return 0;
}