#include<bits/stdc++.h> 
using namespace std;
typedef long long ll;
template<typename T1,typename T2> bool chmin(T1 &a,T2 b){if(a<=b)return 0; a=b; return 1;}
template<typename T1,typename T2> bool chmax(T1 &a,T2 b){if(a>=b)return 0; a=b; return 1;}
int dx[4]={0,1,-1,0};
int dy[4]={1,0,0,-1};
long double eps = 1e-6;
long double pi = acos(-1);


signed main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(20);

    ll n;
    cin>>n;
    ll a[n];
    for(int i=0;i<n;i++){
        cin>>a[i];
    }
    ll lmi[n]={}, rmi[n]={};
    set<ll> l,r;
    for(int i=0;i<n;i++){
            lmi[i] = a[i];
            rmi[n-1-i] = a[n-1-i];
        if(i){
            chmin(lmi[i],lmi[i-1]);
            chmin(rmi[n-1-i], rmi[n-i]);
        } 
        r.insert(a[i]);
    }
    l.insert(a[0]);
    ll ans = 1e18;
    l.insert(1e18);
    r.insert(1e18);
    r.erase(a[0]);
    for(int i=1;i<n-1;i++){
        r.erase(a[i]);
        auto lma = l.lower_bound(a[i]);
        auto rma = r.lower_bound(a[i]);
        if(lmi[i]<a[i] && rmi[i] < a[i]) chmin(ans,a[i]+lmi[i]+rmi[i]);
        if(*rma>a[i] && *lma > a[i]) chmin(ans,*rma+a[i]+*lma);
        l.insert(a[i]);
    }
    if(ans > 1e9)ans=-1;
    cout << ans << endl;
}