#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)

const int INF = 1<<30;

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  int n;
  cin >> n;
  vector<int> a(n);
  REP (i, n) cin >> a[i];

  set<int> pref, suff;
  REP (i, n) suff.insert(a[i]);

  int ret = INF;
  REP (i, n) {
    suff.erase(a[i]);

    if (pref.size() && suff.size()) {
      // a[i] is minimum
      auto itr = pref.lower_bound(a[i]);
      auto jtr = suff.lower_bound(a[i]);
      if (itr != pref.end() && jtr != suff.end())
        ret = min(ret, a[i] + *itr + *jtr);

      // a[i] is maximum
      if (a[i] > max(*pref.begin(), *suff.begin()))
        ret = min(ret, a[i] + *pref.begin() + *suff.begin());
    }

    pref.insert(a[i]);
  }

  cout << (ret == INF ? -1 : ret) << endl;
  
  return 0;
}