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//#include <stdio.h>
#include <bits/stdc++.h>
//#include <ctime>

using namespace std;
typedef vector<int> VI;
typedef long long LL;
typedef vector<VI> VVI;
typedef vector<LL> VLL;
typedef vector<double> VD;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef vector<PII> VPII;

typedef pair<LL,LL> PLL;
typedef vector <PLL> VPLL;

#define FOR(x, b, e) for(int x = b; x <= (e); ++x)
#define FORD(x, b, e) for(int x = b; x >= (e); --x)
#define REP(x, n) for(int x = 0; x < (n); ++x)
#define VAR(v, n) typeof(n) v = (n)
#define ALL(c) (c).begin(), (c).end()
#define SIZE(x) ((int)(x).size())
#define FOREACH(i, c) for(VAR(i, (c).begin()); i != (c).end(); ++i)
#define PB push_back
#define ST first
#define ND second
#define MP make_pair
#define PF push_front

const int maxn=1e6;

LL tab[maxn];
LL a,n;
LL mak;
int main()
{
	mak=0;
	scanf("%lld", &n);
	REP(i,n)
	{
		scanf("%lld", &a);
		tab[a]++;
	}
	REP(i,maxn-1)
	{
		tab[i+1]+=tab[i]/2;
		tab[i]=tab[i]%2;
		if(tab[i]!=0)
		mak=i;
	}
	printf("%lld\n",mak);

}