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#include <bits/stdc++.h>

using namespace std;

#define MAX_A 500000

int powers [MAX_A];


int main()
    {
        int n, a;
        vector <int> v;
        scanf("%d", &n);
        for (int i = 0; i < n; i++)
            {
                scanf("%d", &a);
                v.push_back(a);
                powers[a]++;
            }

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

        for (int i = MAX_A - 1; i >= 0; i--)
            {
                if (powers[i] > 0)
                    {
                        printf("%d", i);
                        break;
                    }
            }

        return 0;
    }