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#include <iostream>
#include <sstream>
#include <fstream>
#include <string>
#include <vector>
#include <queue>
#include <algorithm>
#include <map>
#include <set>

using namespace std;

typedef long long LL;

#define MAX(a, b) ((a) > (b) ? (a) : (b))
#define MIN(a, b) ((a) < (b) ? (a) : (b))
#define ABS(val) ((val) < 0 ? -(val) : (val))

#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

/* PA2017 SKA */

LL hist[250000] = { 0LL };

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

	LL todo = 0LL;
	REP(i, n)
	{
		int r;
		scanf("%d", &r);
		hist[r] += 1LL;
		todo += 1LL;
	} 

	int i = 0;
	do
	{
		//printf("%d %d %d\n", i, hist[i], todo);
		LL cur = hist[i];
		if (cur > 0LL)
		{
			LL next = cur / 2;
			hist[i + 1] += next;
			todo += (LL)(next - cur);
		}
		i++;	
	} while(todo);

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

	return 0;
}