#include <bits/stdc++.h>
using namespace std;
int INF = 1000000000;
int main(){
  int N;
  cin >> N;
  vector<int> A(N);
  for (int i = 0; i < N; i++){
    cin >> A[i];
  }
  //想定WA2 (場合分けもれ)
  vector<int> L2(N);
  set<int> L;
  for (int i = 0; i < N; i++){
    auto itr = L.upper_bound(A[i]);
    if (itr == L.end()){
      L2[i] = INF;
    } else {
      L2[i] = *itr;
    }
    L.insert(A[i]);
  }
  vector<int> R2(N);
  set<int> R;
  for (int i = N - 1; i >= 0; i--){
    auto itr = R.upper_bound(A[i]);
    if (itr == R.end()){
      R2[i] = INF;
    } else {
      R2[i] = *itr;
    }
    R.insert(A[i]);
  }
  int ans2 = INF;
  for (int i = 1; i < N - 1; i++){
    ans2 = min(ans2, L2[i] + A[i] + R2[i]);
  }
  if (ans2 == INF){
    cout << -1 << endl;
  } else {
    cout << ans2 << endl;
  }
}