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//Tadrion
#include <cstdio>
#include <vector>
#include <iostream>
#include <deque>
#include <map>
#include <set>
#include <string>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <queue>
#include <stack>
#include <algorithm>
#include <utility>
using namespace std;
#define MAX(a,b) ((a) > (b) ? (a) : (b))
#define MIN(a,b) ((a) < (b) ? (a) : (b))
#define CLEAR(x) (memset(x,0,sizeof(x)))
#define SZ(x) ((int)(x).size())
#define ALL(x) (x).begin(),(x).end()
#define VAR(v, n) __typeof(n) v = (n)
#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 FOREACH(i, c) for(VAR(i,(c).begin()); i != (c).end(); ++i)
#define DBG(v) cout<<#v<<" = "<<v<<endl;
#define IN(x,y) ((y).find(x)!=(y).end())
#define ST first
#define ND second
#define PB push_back
#define PF push_front
#define MP make_pair
typedef long long int LL;
typedef pair<int,int> PII;
typedef vector<int> VI;

int n,a,maxx;

char t[300010];

int main() {
    scanf("%d",&n);
    REP(i,n)
    {
        scanf("%d",&a);
        t[a]+=1;

        while(1)
        {
            if(2 == t[a])
            {
                t[a]=0;
                t[a+1]+=1;
                a++;
            }
            else
            {
                break;
            }
        }

    }

    FOR(i,0,300000)
    {
        if(t[i]) maxx = i;
    }

    printf("%d\n",maxx);

  return 0;
}