#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i=0; i<n; i++)
#define pb push_back
#define int long long

int N;
int A[200100];
 
signed main() {
    cin.tie(0); ios::sync_with_stdio(false);
    cin >> N;
    rep(i, N) cin >> A[i];
    multiset<int> ls, rs;
    ls.insert(A[0]);
    ls.insert(1000000000000);
    for (int i=2; i<N; i++) rs.insert(A[i]);
    rs.insert(1000000000000);
    
    int ans = 1000000000000;
    for (int i=1; i<N-1; i++) {
        int lm = *ls.begin(), rm = *rs.begin();
        if (A[i]>lm && A[i]>rm) ans = min(ans, lm+A[i]+rm);
        int ln = *ls.upper_bound(A[i]), rn = *rs.upper_bound(A[i]);
        ans = min(ans, ln+A[i]+rn);
        ls.insert(A[i]);
        rs.erase(rs.find(A[i+1]));
    }
    if (ans==1000000000000) cout << -1 << endl;
    else cout << ans << endl;
}