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#include <bits/stdc++.h>
using namespace std;

const int N = 1e6 + 5;
int n, a[N];

int main()
{
  scanf("%d", &n);
  for (int i = 0; i < n; i++)
  {
    int x; scanf("%d", &x);
    a[x]++;
  }
  int res = 0;
  for (int i = 0; i < N; i++)
  {
    if (a[i] > 0) res = i;
    while (a[i] >= 2)
    {
      a[i+1]++;
      a[i] -= 2;
    }
  }
  printf("%d\n", res);
  return 0;
}