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#include <set>
#include <list>
#include <map>
#include <stack>
#include <bitset>
#include <string>
#include <queue>
#include <deque>
#include <cmath>
#include <vector>
#include <climits>
#include <iostream>
#include <algorithm>

#define F first
#define S second
#define MP make_pair
#define PB push_back

using namespace std;

typedef pair < int, int > PII;
typedef long long LL;
typedef vector < int > VI;
typedef vector < PII > VPII;

int n, a, wyn;
int pot[ 1000007 ];

//****************************************************************************************************************************************************************************************************************************************
int main()
{
	scanf( "%d", &n );
	
	for( int i = 0; i < n; i++ )
	{
		scanf( "%d", &a );
		
		pot[ a ]++;
	}
	
	for( int i = 0; i < 1000000; i++ )
	{
		if( pot[ i ] )
			wyn = i;
		
		pot[ i + 1 ] += pot[ i ] / 2;
	}
	
	printf( "%d", wyn );
	
	return 0;
}
//****************************************************************************************************************************************************************************************************************************************