#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); i++)
#define ALL(v) (v).begin(), (v).end()
using ll = long long;
using P = pair<int, int>;
constexpr int INF = 1e9;
constexpr long long LINF = 1e18;
constexpr long long MOD = 1e9 + 7;

signed main() {
    int n;
    cin >> n;
    set<int> L, R;
    int a[n];
    rep(i, n) {
        cin >> a[i];
        if (i) R.emplace(a[i]);
    }
    L.emplace(a[0]);
    int ans = INF;
    for (int i = 1; i < n - 1; i++) {
        auto litr = L.upper_bound(a[i]);
        auto ritr = R.upper_bound(a[i]);
        if(litr != L.end() && ritr != R.end()){
            ans = min(ans, *litr + a[i] + *ritr);
        }
        if(*L.begin() < a[i] && a[i] > *R.begin()){
            ans = min(ans, *L.begin() + a[i] + *R.begin());
        }
        L.emplace(a[i]);
        R.erase(a[i]);
    }
    cout << (ans != INF ? ans : -1) << endl;
    return 0;
}