#include <iostream>
#include <vector>

using namespace std;

vector<bool> number(201760, false);

void add(int pos) {
    if (!number[pos]) {
        number[pos] = true;
    } else {
        while (number[pos]) {
            number[pos] = false;
            pos++;
        }
        number[pos] = true;
    }
}

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

    int z;
    cin >> z;

    long long num;

    while (z--) {
        cin >> num;
        add(num);
    }


    int size = number.size()-1;
    for(int i = size; i>=0;i-- ){
        if(number[i] == true){
            cout<<i<<endl;
            return 0;
        }
    }
    cout<<"0"<<endl;
}