#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < (n);i++)
#define sz(x) int(x.size())
typedef long long ll;
typedef long double ld;
typedef pair<int,int> P;
typedef pair<ll, int> PL;
constexpr ll INF = (1LL << 60);

int main() {
  int n;
  cin >> n;
  vector<ll> a(n);
  rep(i,n) cin >> a[i];
  vector<ll> left(n + 1, INF), right(n + 1, INF);

  for (int i = 0; i < n; i++) {
    left[i + 1] = min(left[i], a[i]);
  }

  for (int i = n - 1; i >= 0; i--) {
    right[i] = min(right[i + 1], a[i]);
  }

  ll res = INF;

  for (int i = 1; i < n - 1; i++) {
    if (left[i] == right[i + 1]) continue;
    ll mx = max(left[i], right[i + 1]);
    ll mi = min(left[i], right[i + 1]);
    mx = max(a[i], mx);
    mi = min(a[i], mi);
    if (mi == a[i] || mx == a[i]) {
      
      res = min(res, a[i] + left[i] + right[i + 1]);
    }
  }
  cout << (res == INF ? -1 : res) << endl;
  return 0;
}