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/* You can't connect the dots looking forward 
   you can only connect them looking backwards. */

#include<iostream>
#include<vector>
#include<map>
#include<set>
#include<algorithm>
#define ll long long
#define ld long double
#define ull unsigned long long
#define boost ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);cout.precision(10);cout << fixed;
#define dbset(x) for(int i=0 ; i<x.size(); i++) cerr << x[i] << " "; cerr << endl;
#define inf 1000000007
#define INF 1000000000000000000LL
#define PI 3.14159265358979323846
#define mod 1000000007
#define mod1 1000696969
#define flusz fflush(stdout);
#define VI vector<int>
#define VPI vector < pair<int,int> >
#define PII pair<int, int>
#define BIT bitset<N>
#define st first
#define nd second
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define endl '\n'
#define REP(x, y) for(int x = 0; x < (y); ++x)
#define FOR(x, y, z) for(int x = y; x <= (z); ++x)
#define FORR(x, y, z) for(int x = y; x >= (z); --x)
using namespace std;

template<class TH> void _dbg(const char *sdbg, TH h){cerr<<sdbg<<"="<<h<<"\n";}
template<class TH, class... TA> void _dbg(const char *sdbg, TH h, TA... a) {
  while(*sdbg!=',')cerr<<*sdbg++;cerr<<"="<<h<<","; _dbg(sdbg+1, a...);
}
#define debug(...) _dbg(#__VA_ARGS__, __VA_ARGS__)

const int N = 5 * 100*1000 + 7;

int t[N];

int n,res,x;

int test;

void solve()
{
	cin >> n;

	FOR(i,1,n){
		cin >> x;
		t[x]++;
	}

	FOR(i,1,300*1000){
		t[i] += t[i-1]/2;

		if (t[i]){
			res = max(res,i);
		}
	}

	cout << res;

    return;
}

int32_t main()
{
    boost

    test=1;

    while(test--)
    {
        solve();
    }

  return 0;
}