#include <iostream>
#include <algorithm>
#include <iomanip>
#include <vector>
#include <queue>
#include <set>
#include <map>

using namespace std;
typedef long long ll;
int N;
int A[200000];

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(10) << fixed;
    cin >> N;
    for(int i = 0; i < N; i++) {
        cin >> A[i];
        A[i] *= -1;
    }
    int ans = -1e9;
    multiset<int> stl, str;
    stl.insert(A[0]);
    for(int i = 2; i < N; i++) str.insert(A[i]);
    for(int i = 1; i < N-1; i++){
        // < >
        auto l = lower_bound(stl.begin(), stl.end(), A[i]);
        auto r = lower_bound(str.begin(), str.end(), A[i]);
        if(l != stl.begin() && r != str.begin()){
            l--; r--;
            if(*l != *r){
                ans = max(ans, *l+*r+A[i]);
            }else{
                if(l != stl.begin()){
                    l--;
                    ans = max(ans, *l+*r+A[i]);
                    l++;
                }
                if(r != stl.begin()){
                    r--;
                    ans = max(ans, *l+*r+A[i]);
                    r++;
                }
            }
        }
        // > <
        l = stl.end(); l--;
        r = str.end(); r--;
        if(*l > A[i] && *r > A[i]){
            if(*l != *r){
                ans = max(ans, *l+*r+A[i]);
            }else{
                if(l != stl.begin()){
                    l--;
                    if(*l > A[i]) ans = max(ans, *l+*r+A[i]);
                    l++;
                }
                if(r != stl.begin()){
                    r--;
                    if(*r > A[i]) ans = max(ans, *l+*r+A[i]);
                    r++;
                }
            }
        }
        stl.insert(A[i]);
        str.erase(str.find(A[i+1]));
    }
    if(ans == -1e9){
        cout << -1 << endl;
    }else{
        cout << -ans << endl;
    }
}