#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define rep(i, n) for (int i = 0; i < (n); i++)
#define P pair<int, int>

const int INF = 1001001001;

int main() {
  int n;
  cin >> n;
  vector<int> a(n);
  rep(i,n) cin >> a[i];
  vector<int> mxl(n), mxr(n), mnl(n, INF), mnr(n, INF);

  set<int> sl, sr;
  for (int i = 1; i < n; i++) {
    mnl[i] = min(mnl[i-1], a[i-1]);
    sl.insert(a[i-1]);
    auto it = upper_bound(sl.begin(), sl.end(), a[i]);
    if (it == sl.end()) mxl[i] = INF;
    else mxl[i] = *it;
  }
  for (int i = n-2; i >= 0; i--) {
    mnr[i] = min(mnr[i+1], a[i+1]);
    sr.insert(a[i+1]);
    auto it = upper_bound(sr.begin(), sr.end(), a[i]);
    if (it == sr.end()) mxr[i] = INF;
    else mxr[i] = *it;
  }


  int ans = INF;
  for (int i = 1; i < n-1; i++) {
    if (a[i] > mnl[i] && a[i] > mnr[i]) {
      ans = min(ans, a[i]+mnl[i]+mnr[i]);
    }
    if (a[i] < mxl[i] && a[i] < mxr[i]) {
      ans = min(ans, a[i]+mxl[i]+mxr[i]);
    }
  }
  if (ans == INF) ans = -1;
  cout << ans << endl;


}