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

typedef long long ll;
#define REP(i,n) for(int i=0,_n=(int)(n);i<_n;++i)
#define ALL(v) (v).begin(),(v).end()
#define CLR(t,v) memset(t,(v),sizeof(t))
template<class T1,class T2>ostream& operator<<(ostream& os,const pair<T1,T2>&a){return os<<"("<<a.first<<","<<a.second<< ")";}
template<class T>void pv(T a,T b){for(T i=a;i!=b;++i)cout<<(*i)<<" ";cout<<endl;}
template<class T>void chmin(T&a,const T&b){if(a>b)a=b;}
template<class T>void chmax(T&a,const T&b){if(a<b)a=b;}

ll nextLong() { ll x; scanf("%lld", &x); return x;}

const ll INF = 1001001001;

ll solve(vector<int> A) {
  const int N = A.size();

  vector<int> left(N), right(N);
  left[0] = A[0];
  for (int i = 1; i < N; i++) left[i] = min(left[i-1], A[i]);
  right[N-1] = A[N-1];
  for (int i = N-2; i >= 0; i--) right[i] = min(right[i+1], A[i]);
  // pv(ALL(A));
  // pv(ALL(left));
  // pv(ALL(right));


  ll res = INF;
  for (int i = 1; i < N - 1; i++) {
    if (left[i-1] < A[i] && A[i] > right[i+1]) {
      ll val = left[i-1] + A[i] + right[i+1];
      chmin(res, val);
    }
  }

  return res;

}

ll solve2(vector<int> A) {
  const int N = A.size();
  ll res = INF;

  set<int> left;
  set<int> right;
  REP(i, N) right.insert(A[i]);
  for (int i = 0; i < N; i++) {
    right.erase(A[i]);
    if (i - 1 >= 0 && i + 1 < N) {
      auto it1 = left.lower_bound(A[i]);
      auto it2 = right.lower_bound(A[i]);
      if (it1 != left.end() && it2 != right.end()) {
        ll val = (*it1) + A[i] + (*it2);
        chmin(res, val);
      }
    }
    left.insert(A[i]);
  }

  return res;
}


int main2() {
  int N = nextLong();
  vector<int> A(N);
  REP(i, N) A[i] = nextLong();

  ll ans1 = solve(A);
  ll ans2 = solve2(A);

  ll ans = min(ans1, ans2);
  if (ans == INF) ans = -1;
  cout << ans << endl;
  return 0;
}

int main() {

#ifdef LOCAL
  for (;!cin.eof();cin>>ws)
#endif
    main2();
  return 0;
}