#include <iostream>
#include <map>
#include <algorithm>

using namespace std;

int main() {
    int coins = 0;
    cin>>coins;

    int values[coins];
    map<int, int> val;
    for (int i = 0; i < coins; i++) {
        cin>>values[i];
        val[values[i]]++;
    }

    int max = 0;
    for_each(val.begin(), val.end(), [&val, &max](pair<const int, int>& p){
        //value : amount
        int carry = 0;
        carry = p.second/2;
        if(carry != 0)
            val[p.first+1] += carry;
        if (p.first > max)
            max = p.first;
    });

    cout<<max;

    return 0;
}