#include <bits/stdc++.h>
using namespace std;
#define reps(i,s,n) for(int i = s; i < n; i++)
#define rep(i,n) reps(i,0,n)
#define Rreps(i,n,e) for(int i = n - 1; i >= e; --i)
#define Rrep(i,n) Rreps(i,n,0)
#define ALL(a) a.begin(), a.end()
#define fi first
#define se second
typedef long long ll;
typedef vector<ll> vec;
typedef vector<vec> mat;

ll N,M,H,W,Q,K,A,B;
string S;
const ll MOD = 998244353;
//const ll MOD = (1e+9) + 7;
typedef pair<ll, ll> P;
const ll INF = (1LL<<58);

template<class T> bool chmin(T &a, const T &b){
    if(a > b) {a = b; return true;}
    else return false;
}
template<class T> bool chmax(T &a, const T &b){
    if(a < b) {a = b; return true;}
    else return false;
}


int main() {
    cin>>N;
    set<ll> l, r;
    vec a(N);
    rep(i,N) {
        cin>>a[i];
        i == 0 ? l.insert(a[i]) : r.insert(a[i]);
    }
    r.erase(a[1]);
    ll res = INF;
    reps(i,1,N - 1){
        if(*l.begin() < a[i] && *r.begin() < a[i]) chmin(res, a[i] + *l.begin() + *r.begin());
        if(l.lower_bound(a[i]) != l.end() && r.lower_bound(a[i]) != r.end()){
            chmin(res, a[i] + *l.lower_bound(a[i]) + *r.lower_bound(a[i]));
        }
        l.insert(a[i]);
        r.erase(a[i+1]);
    }
    cout<<(res == INF ? -1 : res)<<endl;
}