#include <bits/stdc++.h>
using namespace std;

int main() {
    int n;
    cin >> n;

    vector<int> count(81, 0);
    for (int i = 0; i < n; ++i) {
        int num;
        cin >> num;
        count[num]++;
    }

    for (int i = 1; i <= 80; ++i) {
        if (count[i] >= 2) {
            count[i + 1] += count[i] / 2;
            count[i] %= 2;
        }
    }

    int max_num = 0;
    for (int i = 1; i <= 80; ++i) {
        if (count[i] > 0) {
            max_num = i;
        }
    }

    cout << max_num << endl;

    return 0;
}