#include <algorithm>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
using namespace std;
#define rep(i, n) for(int(i) = 0; (i) < (n); (i)++)
#define FOR(i, m, n) for(int(i) = (m); (i) < (n); (i)++)
#define All(v) (v).begin(), (v).end()
#define pb push_back
#define MP(a, b) make_pair((a), (b))
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
const int INF = 1 << 30;
const ll LINF = 1LL << 60;
const int MOD = 1e9 + 7;

int main() {
    int N;
    cin >> N;
    vector<int> A(N);
    rep(i, N) cin >> A[i];
    set<int> left, right;
    rep(i, N) right.insert(A[i]);
    int res = INF;
    for(int i = 0; i < N - 1; i++) {
        right.erase(A[i]);
        if(i > 0) {
            left.insert(A[i - 1]);
            auto litr = left.lower_bound(A[i]), ritr = right.lower_bound(A[i]);
            if(litr != left.end() && ritr != right.end()) {
                res = min(res, *litr + *ritr + A[i]);
            }
            auto lmin = left.begin(), rmin = right.begin();
            if(*lmin < A[i] && *rmin < A[i]) {
                res = min(res, A[i] + *rmin + *lmin);
            }
        }
    }
    cout << (res == INF ? -1 : res) << endl;
    return 0;
}