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#include <cstdio>
#include <algorithm>
#include <unordered_map>

using namespace std;

int n, a;
int act_max;
unordered_map<int, int> M;

int main() {
  scanf("%d", &n);
  for(int i = 0; i < n; ++i) {
    scanf("%d", &a);
    act_max = max(a, act_max);
    if(M.count(a) == 0) {
      M[a] = 1;
    } else M[a] = M[a] + 1;
  }
  int act = 0;
  while(act <= act_max) {
    if(M.count(act) > 0) {
      int to_move = M[act] / 2;
      if(to_move > 0) {
        act_max = max(act + 1, act_max);
      }
      if(M.count(act + 1) == 0) {
        M[act + 1] = to_move;
      } else M[act + 1] += to_move;
    }
    ++act;
  }
  printf("%d\n", act_max);

  return 0;
}