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#include <iostream>

using namespace std;

int main() {
    ios_base::sync_with_stdio(0);

    int n;

    cin >> n;

    int * amount = new int [300000];

    for(int i = 0; i < 300000; i++)
        amount[i] = 0;

    for(int i = 0; i < n; i++) {
        int temp;

        cin >> temp;

        amount[temp]++;
    }

    int max = 0;

    for(int i = 0; i < 299999; i++) {
        amount[i + 1] += (amount[i] / 2);

        if(amount[i + 1])
            max = i + 1;
    }

    cout << max << endl;

    return 0;
}