#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#define rep(i, j, n) for (i64 i = (j); i < (n); ++i)
#define rrep(i, j, n) for (i64 i = (n)-1; i >= (j); --i)
using namespace std;
using i64 = int64_t;
constexpr int INF = 1 << 30;

int main()
{
  int n;
  cin >> n;
  int *a = new int[n];
  rep(i, 0, n) cin >> a[i];
  int ans = INF;

  set<int> l;
  set<int> r;

  // min
  vector<int> mr(n, INF);
  rrep(i, 1, n) mr[i - 1] = min(a[i], mr[i]);
  int ml = a[0];

  // a[i]が一番でかい
  rep(i, 1, n - 1)
  {
    if (a[i] > ml && a[i] > mr[i])
      ans = min(ans, ml + a[i] + mr[i]);
    ml = min(ml, a[i]);
  }

  // a[i]が一番小さい
  rep(i, 1, n) r.insert(a[i]);
  l.insert(a[0]);
  rep(i, 1, n - 1)
  {
    r.erase(a[i]);
    auto li = l.lower_bound(a[i]);
    auto ri = r.lower_bound(a[i]);
    if (li != l.end() && ri != r.end())
      ans = min(ans, a[i] + *ri + *li);
    l.insert(a[i]);
  }

  if (ans == INF)
    cout << -1;
  else
    cout << ans;
  delete[] a;
  return 0;
}