#include <iostream>
#include <algorithm>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <bitset>
#include <cmath>

static const int MOD = 1000000007;
using ll = long long;
using u32 = unsigned;
using u64 = unsigned long long;
using namespace std;

template<class T> constexpr T INF = ::numeric_limits<T>::max()/32*15+208;

int main() {
    int n;
    cin >> n;
    vector<int> v(n);
    for (auto &&i : v) scanf("%d", &i);
    vector<int> m(n);
    m[0] = INF<int>;
    for (int i = 1; i < n; ++i) {
        m[i] = min(m[i-1], v[i-1]);
    }
    int val = INF<int>, ans = INF<int>;
    for (int i = n - 1; i >= 0; --i) {
        if(max(m[i], val) < v[i]) ans = min(ans, m[i]+val+v[i]);
        val = min(val, v[i]);
    }
    set<int> s;
    for (int i = 0; i < n; ++i) {
        auto x = s.lower_bound(v[i]);
        if(x == s.end()) m[i] = INF<int>;
        else m[i] = *x;
        s.emplace(v[i]);
    }
    s.clear();
    for (int i = n-1; i >= 0; --i) {
        auto x = s.lower_bound(v[i]);
        if(x != s.end()) ans = min(ans, *x+v[i]+m[i]);
        s.emplace(v[i]);
    }
    if(ans == INF<int>) puts("-1");
    else cout << ans << "\n";
    return 0;
}