#include<iostream>
#include<algorithm>
#include<vector>
#include<string>
#include<utility>
#include<map>
#include<set>
#include<queue>
#include<stack>
#include<functional>
#include<math.h>
#include<random>
#include <bitset>
using namespace std;
#define N (1000000000+7)
//#define N 998244353
#define INF 1e16
typedef long long ll;
typedef pair<int,int> P;
typedef pair<int,P> Q;

const int inf = (int)1e9; 



int main(void){
    int n;
    cin>>n;
    vector<ll>a(n);
    for(int i=0;i<n;i++)cin>>a[i];
    reverse(a.begin(),a.end());
    set<ll>s1,s2;
    s1.insert(a[0]);
    for(int i=1;i<n;i++)s2.insert(a[i]);
    ll ans = (ll)INF;
    for(int i=1;i<n-1;i++){
        s2.erase(a[i]);
        auto itr1 = s1.upper_bound(a[i]);
        auto itr2 = s2.upper_bound(a[i]);
        if(itr1!=s1.end()&&itr2!=s2.end()){
            ans = min(ans,a[i]+*(itr1)+*(itr2));
        }
        itr1 = s1.lower_bound(a[i]);
        itr2 = s2.lower_bound(a[i]);
        if(itr1==s1.begin()){
            s1.insert(a[i]);
            continue;
        }
        if(itr2==s2.begin()){
            s1.insert(a[i]);
            continue;
        }
        ans = min(ans,a[i]+*(s1.begin())+*(s2.begin()));
        s1.insert(a[i]);
    }
    if(ans == (ll)INF)cout<<-1<<endl;
    else cout<<ans<<endl;
    return 0;
}