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#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <stack>
#include <cstdio>
#include <set>
#include <map>
#include <string>
#include <queue>
#include <stack>
using namespace std;

typedef long long int LL;
typedef long double LD;
typedef vector<int> VI;
typedef vector<LL> VLL;
typedef vector<LD> VLD;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef vector<PII> VPII;

const int INF = 1000000001;
const LD EPS = 10e-9;

#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 FORE(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 abs(a) ((a)<0 ? -(a) : (a))
#define max(a, b) ((a) > (b) ? (a) : (b))
#define min(a, b) ((a) < (b) ? (a) : (b))

const int MAX_N = 1000005;
const int MAX_P = 202000;

int n, a[MAX_N], p[MAX_P+10], res;

int main()
{
	scanf("%d", &n);
	REP(i, n)
	{
		scanf("%d", &a[i]);
		p[a[i]]++;
	}
	
	for(int i = 0; i < MAX_P; ++i)
	{
		if(p[i] == 0)
			continue;
			
		//cout << "i: " << i << ", p[i]: " << p[i] << endl;	
		res = i;
		
		p[i+1] += (p[i]/2); 
		p[i] %= 2;
	}
	
	printf("%d\n", res);
	
	//system("pause");
    return 0;
}