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

bool x[201740], f;

int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int n, a;
    cin >> n;
    for(int i = 0; i < n; i++){
        cin >> a;
        while(!f){
            if(x[a] == 0){
                x[a] = 1;
                f = 1;
            }
            else{
                x[a] = 0;
                a++;
            }
        }
        f = 0;
    }
    for(int i = 201740; i >= 0; i--)
        if(x[i] == 1){
            cout << i;
            return 0;
        }
}