#include <bits/stdc++.h>
using namespace std;
int main(){
    int N;
    cin >> N;
    vector<int> A(N);
    set<int> sl, sr;
    for(int i = 0; i < N; i++) {
        cin >> A[i];
        sr.insert(A[i]);
    }
    vector<int> ml(N), mr(N), Ml(N), Mr(N);
    ml[0] = A[0];
    mr[N - 1] = A[N - 1];
    Ml[0] = A[0];
    Mr[N - 1] = A[N - 1];
    for(int i = 1; i < N; i++){
        if(ml[i - 1] > A[i]) ml[i] = A[i];
        else ml[i] = ml[i - 1];
    } 
    for(int i = 1; i < N; i++){
        if(mr[N - i] > A[N - 1 - i]) mr[N - 1 - i] = A[N - 1 - i];
        else mr[N - i - 1] = mr[N - i];

    } 
    int ans = 1e9;
    sl.insert(A[0]);
    sr.erase(A[0]);
    for(int i = 1; i < N - 1; i++){
        sr.erase(A[i]);
        if(ml[i - 1] < A[i] && A[i] > mr[i + 1]) ans = min(ans, ml[i - 1] + A[i] + mr[i + 1]);
        auto ite = sl.lower_bound(A[i]), ite2 = sr.lower_bound(A[i]);
        if(ite != sl.end() && ite2 != sr.end()) ans = min(ans, A[i] + *ite + *ite2);
        sl.insert(A[i]);
    }
    int INF = 1e9;
    if(ans == INF){
        cout << -1 << endl;
        return 0;
    }
    cout << ans << endl;
}