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#include <cstdio>
#include <iostream>
#include <algorithm>
#include <cstring>
#include <vector>
#include <set>
#include <map>
#include <cmath>
#include <list>
#include <ctime>
#include <sstream>
#include <queue>
#include <stack>
#include <bitset>
#include <unordered_set>
#include <unordered_map>
using namespace std;
typedef vector<int> vi;
typedef pair<int,int> pii;
typedef long long ll;
typedef short int sint;
#define FOR(x, b, e) for(int x=(b); x<=(e); ++x)
#define FORD(x, b, e) for(int x=((int)(b))-1; x>=(e); --x)
#define REP(x, n) for(int x=0; x<(n); ++x)
#define ALL(c) c.begin(),c.end()
#define SIZE(x) ((int)((x).size()))
#define PB push_back
#define ST first
#define ND second
#define mp(x,y) make_pair(x,y)
#define DEBUG 1
#define debug(x) {if (DEBUG)cerr <<#x <<" = " <<x <<endl; }
#define debugv(x) {if (DEBUG) {cerr <<#x <<" = "; FOREACH(it, (x)) cerr <<*it <<", "; cout <<endl; }}
#define REMAX(a,b) (a)=max((a),(b));
#define REMIN(a,b) (a)=min((a),(b));
#define wez(n) int (n); scanf("%d",&(n));
#define wez2(n,m) int (n),(m); scanf("%d %d",&(n),&(m));

const int N = 2222222;
int tab[N];
int n;

int main() {
	scanf("%d", &n);
	REP(i, n) {
		wez(x)
		++tab[x];
	}
	int najw = 0;
	REP(x, N - 1) {
		if (tab[x] >= 2) {
			tab[x + 1] += (tab[x] / 2);
			tab[x] &= 1;
		}
		if (tab[x]) {
			najw = x;
		}
	}
	printf("%d\n", najw);
	return 0;
}