#include <bits/stdc++.h>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;
typedef unsigned long long ull;

static const int INF = 999999999;
class RMQ {
  int N;
  std::vector<int> dat;

 public:
  RMQ() {}
  void init(int n_) {
    N = 1;
    while (N < n_) N *= 2;
    for (int i = 0; i < 2 * N - 1; i++)
      dat.push_back(INF);
  }
  int query(int a, int b) { return _query(a, b, 0, 0, N); }
  int _query(int a, int b, int k, int l, int r) {
    if (r <= a || b <= l) return INF;
    if (a <= l && r <= b) return dat[k];
    else {
      int vl = _query(a, b, k * 2 + 1, l, (l + r) / 2);
      int vr = _query(a, b, k * 2 + 2, (l + r) / 2, r);

      if (vl < vr) return vl;
      else return vr;
    }
  }
  void update(int i, int x) {
    i += N - 1;
    dat[i] = x;
    while (i > 0) {
      i = (i - 1) / 2;
      if (dat[i * 2 + 1] < dat[i * 2 + 2]) {
        dat[i] = dat[i * 2 + 1];
      } else {
        dat[i] = dat[i * 2 + 2];
      }
    }
  }
};

int main(){
  int N;
  cin >> N;
  vector<pair<int,int>> v;
  rep(i,N){
    int a;
    cin >> a;
    v.emplace_back(a,i);
  }
  sort(ALLOF(v));

  int ret = INF;
  {
    RMQ rmq;
    rmq.init(N+5);
    rep(i,v.size()){
      int x = v[i].first;
      int idx = v[i].second;
      int lhs = rmq.query(0,idx);
      int rhs = rmq.query(idx+1, N);
      ret = min(ret, lhs + x + rhs);
      rmq.update(idx, x);
    }
  }
  {
    RMQ rmq;
    rmq.init(N+5);
    for(int i=v.size()-1; i>=0; i--){
      int x = v[i].first;
      int idx = v[i].second;
      int lhs = rmq.query(0,idx);
      int rhs = rmq.query(idx+1, N);
      ret = min(ret, lhs + x + rhs);
      rmq.update(idx, x);
    }
  }

  if(ret == INF) cout << -1 << endl;
  else cout << ret << endl;

  return 0;
}