#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];
  }
  int ans = INF;
  for (int i = 0; i < N; i++){
    for (int j = i + 1; j < N; j++){
      for (int k = j + 1; k < N; k++){
        if ((A[i] < A[j] && A[j] > A[k]) || (A[i] > A[j] && A[j] < A[k])){
          ans = min(ans, A[i] + A[j] + A[k]);
        } 
      }
    }
  }
  if (ans == INF){
    cout << -1 << endl;
  } else {
    cout << ans << endl;
  }
}