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

typedef long long LL;
typedef long double LD;
typedef unsigned long long ULL;
typedef vector<int> VI;
typedef set<int> SI;
typedef pair<int, int> PII;
typedef vector<pair<int, int> > VPII;

const int INF = 1000000001;
const LD EPS = 1e-9;
const int MOD = 1000000007;
const LL LLINF = 1000000000000000001;

//813437586

#define FOR(i, b, e) for(int i = b; i <= e; i++)
#define FORD(i, b, e) for(int i = b; i >= e; i--)
#define ALL(c) (c).begin(), (c).end()
#define SIZE(x) ((int)(x).size())
#define VAR(v, n) auto v = (n)
#define FOREACH(i, c) for(VAR(i, (c).begin()); i != (c).end(); ++i)

#define MP make_pair
#define PB push_back
#define ST first
#define ND second
#define GGL(x) "Case #" << x << ": "


/*************************** END OF TEMPLATE ***************************/


const int maxv = 300000;
int n;
int x[maxv];

int main()
{
	scanf("%d", &n);


	int maxa = 0;
	FOR(i, 1, n)
	{
		int a;
		scanf("%d", &a);
		x[a]++;
		maxa = max(maxa, a);
	}

	int i = 1;

	while(i <= maxa)
	{
		x[i+1] += x[i]/2;
		i++;
	}
	while(x[i])
	{
		x[i+1] += x[i]/2;
		i++;
	}

	printf("%d", i-1);



}