#include "bits/stdc++.h"
using namespace std;
typedef long long ll;

int main() {
    int n;cin >> n;
    vector<int> a(n);
    for (int i = 0; i < n; i++)
    {
        cin >> a[i];
    }
    int ans = 1000000000;
    for (int i = 0; i < n-2; i++)
    {
        if (a[i] < a[i + 1] && a[i + 1] > a[i + 2]) {
            ans = min(ans,a[i] + a[i + 1] + a[i +2]);
        }
        else if (a[i] > a[i + 1] && a[i + 1] < a[i + 2]) {
            ans = min(ans,a[i] + a[i  +1] + a[i  +2]);
        }
    }
    if (ans == 1000000000) {
        cout<< -1 << endl;
    }
    else {
        cout << ans << endl;
    }
    return 0;
}