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#include <iostream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <climits>
#include <vector>
#include <map>
#include <queue>
#include <string>
#include <cstdio>

#define MOD 1000000007
#define ll long long
#define ld long double
#define pi pair <int, int>
#define pll pair <long long, long long>
#define fi first
#define se second
#define mp make_pair
#define pb push_back

using namespace std;

int ile[300007];
int n, a, maks, d;

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);

    cin >> n;
    for(int i=0; i<n; i++) {
        cin >> a;
        ile[a]++;
    }
    maks=0;
    for(int i=0; i<300000; i++) {
        if(ile[i]>0) {
            maks=i;
        }
        d=ile[i]/2;
        ile[i+1]+=d;
    }
    cout << maks << "\n";
}