#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main(){
    int n;
    cin >> n;
    vector<int> a(n);
    for(auto &p: a) cin >> p;

    vector<vector<int>> vec(5, vector<int>(n));
    for(int i = 0; i < 5; i++) vec[i][0] = a[0];
    for(int i = 0; i < 5; i++) vec[i][n-1] = a[n-1];
    for(int i = 1; i < n; i++){
        vec[0][i] = a[i];
        vec[1][i] = min(vec[1][i-1], a[i]);
        vec[2][i] = max(vec[2][i-1], a[i]);
    }
    for(int i = n-2; i >= 0; i--){
        vec[3][i] = min(vec[3][i+1], a[i]);
        vec[4][i] = max(vec[4][i+1], a[i]);
    }

    int ans = 1001001001;
    for(int i = 1; i < n-1; i++){
        for(int bit = 0; bit < (1 << 2); bit++){
            vector<int> coans;
            coans.push_back(vec[0][i]);
            if(bit & (1 << 0)) coans.push_back(vec[1][i-1]);
            else coans.push_back(vec[2][i-1]);
            if(bit & (1 << 1)) coans.push_back(vec[3][i+1]);
            else coans.push_back(vec[4][i+1]);

            if(coans[0] == min(coans[0], min(coans[1], coans[2]))
            || coans[0] == max(coans[0], max(coans[1], coans[2]))){
                ans = min(ans, coans[0]+coans[1]+coans[2]);
                //cerr << coans[0] << " " << coans[1] << " " << coans[2] << endl;
            }
        }
    }

    if(ans == 1001001001) ans = -1;
    cout << ans << endl;
    return 0;
}