#include <bits/stdc++.h>
using namespace std;
template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}
using Int = long long;
const char newl = '\n';

//INSERT ABOVE HERE
signed main(){
  cin.tie(0);
  ios::sync_with_stdio(0);

  int n;
  cin>>n;

  vector<int> as(n);
  for(int i=0;i<n;i++) cin>>as[i];

  const int INF = 1e9;
  int ans=INF;
  {
    set<int> bf,af(as.begin(),as.end());
    for(int i=0;i<n;i++){
      af.erase(as[i]);

      auto ib=bf.lower_bound(as[i]);
      auto ia=af.lower_bound(as[i]);
      if(ib!=bf.end() and ia!=af.end())
        chmin(ans,*ib+as[i]+*ia);

      if(!bf.empty() and !af.empty())
        if(*bf.begin()<as[i] and *af.begin()<as[i])
          chmin(ans,*bf.begin()+as[i]+*af.begin());

      bf.emplace(as[i]);
    }
  }

  if(ans==INF) ans=-1;
  cout<<ans<<newl;
  return 0;
}