#include <bits/stdc++.h>
#define For(i, a, b) for(int (i)=(int)(a); (i)<(int)(b); ++(i))
#define rFor(i, a, b) for(int (i)=(int)(a)-1; (i)>=(int)(b); --(i))
#define rep(i, n) For((i), 0, (n))
#define rrep(i, n) rFor((i), (n), 0)
#define fi first
#define se second
using namespace std;
typedef long long lint;
typedef unsigned long long ulint;
typedef pair<int, int> pii;
typedef pair<lint, lint> pll;
template<class T> bool chmax(T &a, const T &b){if(a<b){a=b; return true;} return false;}
template<class T> bool chmin(T &a, const T &b){if(a>b){a=b; return true;} return false;}
template<class T> T div_floor(T a, T b){
    if(b < 0) a *= -1, b *= -1;
    return a>=0 ? a/b : (a+1)/b-1;
}
template<class T> T div_ceil(T a, T b){
    if(b < 0) a *= -1, b *= -1;
    return a>0 ? (a-1)/b+1 : a/b;
}

constexpr lint mod = 1e9+7;
constexpr lint INF = mod * mod;
constexpr int MAX = 100010;

int main(){
    int n;
    scanf("%d", &n);
    lint a[n];
    set<lint> L, R;
    rep(i, n) scanf("%lld", &a[i]), R.insert(a[i]);
    lint ans = INF;
    rep(i, n){
        R.erase(a[i]);
        if(0<i && i<n-1){
            if(*L.begin() < a[i] && *R.begin() < a[i]){
                chmin(ans, *L.begin() + a[i] + *R.begin());
            }
            if(*L.rbegin() > a[i] && *R.rbegin() > a[i]){
                chmin(ans, *L.lower_bound(a[i]) + a[i] + *R.lower_bound(a[i]));
            }
        }
        L.insert(a[i]);
    }
    printf("%lld\n", ans < INF ? ans : -1);
}