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#include <iostream>
#include <cstdio>

using namespace std;

int main()
{
    int counts[203000];
    for (int i = 0; i<203000; i++) counts[i] = 0;
    int n;
    scanf("%d", &n);
    for (int i = 0; i<n; i++)
    {
        int a;
        scanf("%d", &a);
        counts[a]++;
    }

    for (int i = 0; i<202999; i++)
    {
        counts[i + 1] += counts[i] / 2;
        counts[i] = counts[i] % 2;
    }

    int maxA = 0;
    for (int i = 0; i<202999; i++)
    {
        if (counts[i] == 1)
        {
            maxA = i;
        }
    }

    cout << maxA;
    return 0;
}