#include <cassert>
#include <cmath>
#include <climits>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <climits>
#include <map>
#include <queue>
#include <set>
#include <cstring>
#include <vector>

using namespace std;
typedef long long ll;

int main() {
  int N;
  cin >> N;
  vector<int> A(N);
  for (int i = 0; i < N; ++i) {
    cin >> A[i];
  }

  vector<int> L(N);
  vector<int> LA;
  vector<int> LL(N, -1);
  vector<int> R(N);
  vector<int> RA;
  vector<int> RR(N, -1);
  int min_v = INT_MAX;

  for (int i = 0; i <= N - 1; ++i) {
    int a = A[i];
    auto it = lower_bound(LA.begin(), LA.end(), a);
    int idx = it - LA.begin();

    if (it != LA.end()) {
      LL[i] = a + LA[idx];
    }
    LA.insert(LA.begin() + idx, a);

    min_v = min(min_v, a);
    L[i] = min_v;
  }

  min_v = INT_MAX;
  for (int i = N - 1; i >= 0; --i) {
    int a = A[i];
    auto it = lower_bound(RA.begin(), RA.end(), a);
    int idx = it - RA.begin();

    if (it != RA.end()) {
      RR[i] = a + RA[idx];
    }
    RA.insert(RA.begin() + idx, a);

    min_v = min(min_v, a);
    R[i] = min_v;
  }

  /*
  for (int i = 0; i < N; ++i) {
    cerr << LL[i] << " ";
  }
  cerr << endl;
  for (int i = 0; i < N; ++i) {
    cerr << RR[i] << " ";
  }
  cerr << endl;
  */

  int ans = INT_MAX;

  for (int i = 1; i <= N - 2; ++i) {
    int a = A[i];
    int l = LL[i];
    int r = RR[i];
    if (l == -1) continue;
    if (r == -1) continue;

    int v = l + r - a;
    ans = min(ans, v);
  }

  for (int i = 1; i <= N - 2; ++i) {
    int a = A[i];
    int l = L[i - 1];
    int r = R[i + 1];
    if (l > a) continue;
    if (r > a) continue;

    int v = a + l + r;
    ans = min(ans, v);
  }


  if (ans == INT_MAX) {
    cout << -1 << endl;
  } else {
    cout << ans << endl;
  }

  return 0;
}