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#include <iostream>

using namespace std;
typedef long long ll;

ll a[202800];
ll p[] = {
            1,
            2,
            4,
            8,
            16,
            32,
            64,
            128,
            256,
            512,
            1024,
            2048,
            4096,
            8192,
            16384,
            32768,
            65536,
            131072,
            262144,
            524288,
            1048576
            };


     

int main()
{
    ios_base::sync_with_stdio(false);

    ll n;
    ll b;
    cin >> n;

    for (int i = 0; i < n; i++)
    {
        cin >> b;
        a[b]++;
    }
    
    ll max = -1;
    
    for (int i = 0; i < 202800; i++)
    {
        if (a[i] > 0)
            max = i;
        else
            continue;

    
        bool wasChange = false;

        do
        {
            wasChange = false;

            for (int j = 1; j < 20; j++) //largest p
            {
                if (p[j] <= a[i] && p[j+1] > a[i])
                {
                    wasChange = true;
                    a[i+j]++;
                    a[i] -= p[j];
                }    
            }
        }
        while (wasChange);

    }

    cout << max << endl;




    return 0;
}