#include <bits/stdc++.h>
using namespace std;
int INF = 1000000000;
int main(){
  //想定WA (場合分けもれ)
  int N;
  cin >> N;
  vector<int> A(N);
  for (int i = 0; i < N; i++){
    cin >> A[i];
  }
  int ans1 = INF;
  vector<int> L1(N);
  L1[0] = A[0];
  for (int i = 1; i < N; i++){
    L1[i] = min(L1[i - 1], A[i]);
  }
  vector<int> R1(N);
  R1[N - 1] = A[N - 1];
  for (int i = N - 2; i >= 0; i--){
    R1[i] = min(R1[i + 1], A[i]);
  }
  for (int i = 1; i < N - 1; i++){
    if (L1[i - 1] < A[i] && A[i] > R1[i + 1]){
      ans1 = min(ans1, L1[i - 1] + A[i] + R1[i + 1]);
    }
  }
  if (ans1 == INF){
    cout << -1 << endl;
  } else {
    cout << ans1 << endl;
  }
}