#include <iostream> #include <vector> #include <algorithm> #include <cmath> #include <string> #include <queue> #include <stack> #include <set> #include <map> #include <iomanip> #include <utility> #include <tuple> #include <functional> #include <bitset> #include <cassert> #include <complex> #include <stdio.h> #include <time.h> #include <numeric> #include <random> #include <unordered_map> #include <unordered_set> #define all(a) a.begin(),a.end() #define rep(i, n) for (ll i = 0; i < (n); i++) #define pb push_back #pragma GCC optimize("O3") #pragma GCC optimize("unroll-loops") using namespace std; typedef long long ll; typedef unsigned long long ull; typedef long double ld; typedef pair<ll, ll> P; typedef complex<ld> com; constexpr int inf = 1000000010; constexpr ll INF = 1000000000000000010; constexpr ld eps = 1e-12; constexpr ld pi = 3.141592653589793238; template<class T, class U> inline bool chmax(T &a, const U &b) { if (a < b) { a = b; return true; } return false; } template<class T, class U> inline bool chmin(T &a, const U &b) { if (a > b) { a = b; return true; } return false; } signed main() { cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); int n; cin >> n; vector<int> a(n); rep(i, n) cin >> a[i]; int ans = inf; set<int> left, right; left.insert(inf); right.insert(inf); for (int i = 1; i < n; i++) right.insert(a[i]); rep(i, n) { auto itr = right.lower_bound(a[i]); auto itl = left.lower_bound(a[i]); if (*itr != inf && *itl != inf) chmin(ans, *itr + *itl + a[i]); itr = left.begin(); itl = right.begin(); if (*itr < a[i] && *itl < a[i]) chmin(ans, *itr + *itl + a[i]); left.insert(a[i]); if (i != n - 1) right.erase(a[i + 1]); } if (ans == inf) cout << "-1\n"; else cout << ans << '\n'; }