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#include <cstdio>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <string>
#include <iostream>
#include <cstring>
#include <cctype>
#include <queue>
#include <list>
#include <cstdlib>
#include <cmath>
#include <deque>
using namespace std;

typedef long long LL;
typedef pair<int,int> para;
typedef vector<int> VI;
typedef vector<vector<int> > VII;
typedef vector<string> VS;

#define PB push_back
#define MP make_pair
#define F first
#define S second
#define FOREACH(a,n) for (__typeof(n.begin())a=n.begin();a!=n.end();++a)
#define FOR(i,a,b) for (int i=(a);i<=(b);++i)
#define FORD(i,a,b) for (int i=(a);i>=(b);--i)
#define REP(i,n) for (int i=0;i<(n);++i)
#define ALL(x) x.begin(),x.end()
#define SIZE(x) ((int)x.size())

int t[1000007];

int main()
{
  int n;
  scanf("%d", &n);	
  REP(i, n) {
    scanf("%d", &t[i]);
  }
  sort(t, t+n);
  int p = 0, c = 0;
  REP(i, n) {
    while (p < t[i]){
      c/=2;
      p += 1;
    }
    if (t[i] == p) {
      c++;
    }
  }
  while(c > 1){
    c /=2;
    p+=1;
  }
  printf("%d\n", p);
  return 0;
}