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#include <iostream>

using namespace std;

const int MAX_EXP = 201718 + 12;

int purse[MAX_EXP];

int main()
{
    int n; cin >> n;
    int max_nom = 0;
    for (int i=0; i<n; ++i)
    {
        int ai; cin >> ai;
        ++purse[ai];
        if (max_nom < ai) max_nom = ai;
    }

    for (int i=0; i < max_nom; ++i)
    {
        purse[i+1] += purse[i] / 2;
        purse[i] %= 2;
    }

    while (purse[max_nom] > 1)
    {
        ++max_nom;
        purse[max_nom] = purse[max_nom-1] / 2;
        purse[max_nom-1] %= 2;
    }

    cout << max_nom << endl;

    return 0;
}