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#include<bits/stdc++.h>
using namespace std;
# ifdef DEB
# define debug(...) fprintf(stderr, __VA_ARGS__)
# else
# define debug(...)
#endif
#define F first
#define S second
#define MP make_pair
#define PB push_back
#define LL long long
#define LD long double
#define PII pair<int, int>
#define PLL pair<LL, LL>
#define pb pop_back
#define VI vector<int>
#define VPI vector<PII>
#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 RE(i,n) FOR(i,1,n)
#define REP(i,n) FOR(i,0,(int)(n)-1)
#define ALL(x) (x).begin(), (x).end()
#define siz(V) ((int)V.size())
const int M = 1024 * 512;

int T[M];
int n, res;

int main()
{
  //ios_base::sync_with_stdio(0);
  scanf("%d", &n);
  for (int i = 0; i < n; i++)
  {
    int a;
    scanf("%d", &a);
    T[a]++;
  }
  for (int i = 0; i < M - 1; i++)
  {
    if (T[i] > 0)
    {
      res = max(res, i);
    }
    T[i + 1] += T[i] / 2;
  }
  printf("%d\n", res);
  return 0;
}