#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;

int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    int n, m;
    cin >> n;
    vector<ll> v;
    for (int i = 0; i < pow(2, n); i++)
    {
        cin >> m;
        v.push_back(m);
    }

    ll a, b, j = 0, k = 0;
    sort(v.begin(), v.end());
    for (int i = 0; i < n; i++)
    {
        j = 0;
        while (j < pow(2, n - i))
        {

            a = v[j + k];
            b = v[j + 1 + k];
            // cout << a << " " << b << " " << j << endl;
            if (b > a + b && b > m && b > a)
            {
                m = b;
            }
            else if (a + b > b && a + b > m && a + b > a)
            {
                m = a + b;
            }
            else if (a > b && a > m && a + b < a)
            {
                m = a;
            }

            v.push_back(a + b);
            j += 2;
        }
        k += j;
    }

    cout << m << "\n";

    return 0;
}