#include <bits/stdc++.h>




int main(){
  int N;

  while(std::cin >> N){
    std::vector<int> A(N);
    for(int i = 0; i < N; ++i) std::cin >> A[i];

    int ans = INT_MAX;

    std::set<int> right, left;

    for(int i = 0; i < N; ++i) right.insert(A[i]);

    for(int i = 0; i < N; ++i){
      int b = A[i];

      right.erase(b);

      if(left.size() and right.size()){
        if(*left.begin() < b and *right.begin() < b){
          ans = std::min(ans, *left.begin() + b + *right.begin());
        }
      }
      
      {
        auto lit = left.lower_bound(b);
        auto rit = right.lower_bound(b);

        if(lit != left.end() and rit != right.end()){
          ans = std::min(ans, *lit + b + *rit);
        }
      }

      left.insert(b);
    }
    
    std::cout << (ans == INT_MAX ? -1 : ans) << "\n";
  }

  return 0;
}