#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(int)(n);i++)
using namespace std;
using ll = long long ;
using P = pair<int,int> ;
using pll = pair<long long,long long>;
constexpr int INF = 1e9;
constexpr long long LINF = 1e17;
constexpr int MOD = 1000000007;
constexpr double PI = 3.14159265358979323846;

int main(){
    int n;
    cin >> n;
    vector<ll> a(n);
    rep(i,n) cin >> a[i];
    vector<ll> minr(n),minl(n);
    ll mn = INF;
    rep(i,n){
        minr[i] = mn;
        mn = min(mn,a[i]);
    }
    mn = INF;
    for(int i=n-1;i>=0;i--){
        minl[i] = mn;
        mn = min(mn,a[i]);
    }
    ll ans = LINF;
    for(int i=1;i<n-1;i++){
        ll res = a[i];
        if(minr[i] < a[i] && minl[i] < a[i]){
            ans = min(ans,res + minr[i] + minl[i]);
        }
    }

    vector<ll> bir(n,-1),bil(n,-1);
    set<ll> st;
    rep(i,n){
        auto it = upper_bound(st.begin(),st.end(),a[i]);
        if(it!=st.end()) bir[i] = *it;
        st.insert(a[i]);
    }
    set<ll> stt;
    for(int i=n-1;i>=0;i--){
        auto it = upper_bound(st.begin(),st.end(),a[i]);
        if(it!=st.end()) bil[i] = *it;
        stt.insert(a[i]);
    }

    for(int i=1;i<n-1;i++){
        if(bir[i]==-1||bil[i]==-1) continue;
        ans = min(ans,a[i] + bir[i] + bil[i]);
    }

    if(ans==LINF) cout << -1 << endl;
    else cout << ans << endl;
    return 0;
}