#include <bits/stdc++.h>
using namespace std;
typedef pair<int,int> P;
typedef long long ll;
typedef long double ld;
const int inf=1e9+7;
const ll longinf=1LL<<60;
#define REP(i,m,n) for(int i=(int)(m) ; i < (int) (n) ; ++i )
#define rep(i,n) REP(i,0,n)
#define F first
#define S second
constexpr char ln = '\n';

const int mx=200010;
const ll mod=1e9+7;

int main(){
  int n;
  cin >> n;
  vector<int> c(n);
  set<int> str,stl;
  rep(i,n){
    cin >> c[i];
    str.insert(c[i]);
  }
  int ans = inf;
  stl.insert(c[0]);
  str.erase(c[0]);
  REP(i,1,n-1){
    str.erase(c[i]);
    auto posl = stl.lower_bound(c[i]);
    auto posr = str.lower_bound(c[i]);
    if(posl!=stl.begin() && posr!=str.begin()){
      ans = min(ans, c[i]+*stl.begin()+*str.begin());
    }
    if(posl!=stl.end() && posr!=str.end()){
      ans = min(ans, c[i]+*posl+*posr);
    }
    stl.insert(c[i]);
  }
  if(ans==inf) ans = -1;
  cout << ans << ln;
  return 0;
}