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

typedef long long ll;

int main() {
    int N, ans = 1e9;
    cin >> N;
    vector<int> A(N);
    set<int> l, r;
    rep(i, N) {
        cin >> A[i];
    }
    rep(i, N - 1) r.insert(A[i + 1]);
    rep(i, N - 2) {
        l.insert(A[i]);
        r.erase(A[i + 1]);
        auto a = l.begin(), b = r.begin();
        if (*a < A[i + 1] && A[i + 1] > *b) {
            ans = min(ans, *a + A[i + 1] + *b);
        }
        a = l.upper_bound(A[i + 1]);
        b = r.upper_bound(A[i + 1]);
        if (a != l.end() && b != r.end()) {
            ans = min(ans, *a + A[i + 1] + *b);
        }
    }
    if (ans == 1e9) ans = -1;
    cout << ans << "\n";
}