#include <iostream>
using namespace std;

const unsigned int MAX = 201718 + 20;
unsigned int coins[MAX];

int main()
{
   std::ios_base::sync_with_stdio(false);

   unsigned int n, x, m=0;
   cin >> n;

   for(auto i=0u; i<n; ++i)
   {
      cin >> x;
      ++(coins[x]);
   }

   x = coins[0];
   unsigned int *coin = coins;
   for(auto i=1u; i<MAX; ++i)
   {
      x = (x>>1) + *(++coin);
      m = (x) ? i : m;
   }

   cout << m << endl;
   return 0;
}