#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
const int INF = 0x3f3f3f3f;
const ll LINF = 0x3f3f3f3f3f3f3f3fLL;
const double EPS = 1e-8;
const int MOD = 1000000007;
// const int MOD = 998244353;
const int dy[] = {1, 0, -1, 0}, dx[] = {0, -1, 0, 1};
const int dy8[] = {1, 1, 0, -1, -1, -1, 0, 1}, dx8[] = {0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U> inline bool chmax(T &a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U> inline bool chmin(T &a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    cout << fixed << setprecision(20);
  }
} iosetup;

int main() {
  int n; cin >> n;
  vector<int> a(n); REP(i, n) cin >> a[i];
  vector<int> mn_l(n, INF), mn_r(n, INF), mx_l(n, -INF), mx_r(n, -INF);
  set<int> st{a[0]};
  FOR(i, 1, n) {
    mn_l[i] = min(mn_l[i - 1], a[i - 1]);
    auto it = st.lower_bound(a[i]);
    if (it != st.end()) mx_l[i] = *it;
    st.emplace(a[i]);
  }
  st = {a[n - 1]};
  for (int i = n - 2; i >= 0; --i) {
    mn_r[i] = min(mn_r[i + 1], a[i + 1]);
    auto it = st.lower_bound(a[i]);
    if (it != st.end()) mx_r[i] = *it;
    st.emplace(a[i]);
  }
  int ans = INF;
  FOR(i, 1, n - 1) {
    if (mn_l[i] < a[i] && mn_r[i] < a[i]) chmin(ans, mn_l[i] + a[i] + mn_r[i]);
    if (mx_l[i] > a[i] && mx_r[i] > a[i]) chmin(ans, mx_l[i] + a[i] + mx_r[i]);
  }
  cout << (ans == INF ? -1 : ans) << '\n';
  return 0;
}