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// Arkadiusz Roussau
// PO2017 - Skarbonka [B]
#include <iostream>
#include <cstdio>
using namespace std;

const int N = 300000;

int denominations[N];
int number_of_coins, denomination, res = 0;


int main() {
    ios_base::sync_with_stdio(0);
    
    cin >> number_of_coins;
    
    for (int i = 0; i < number_of_coins; ++i) {
        cin >> denomination;
        
        denominations[denomination]++;
    }
    
    for (int i = 0; i < N - 1; ++i) {
        denominations[i + 1] += (denominations[i] / 2);
        denominations[i] %= 2;
    }
    
    for (int i = (N - 1); i >= 0; --i) {
        if (denominations[i] > 0) {
            res = i;
            break;
        }
    }
    
    cout << res << "\n";
    
    return 0;
}