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#include <cassert>
#include <cstdio>
#include <vector>

using namespace std;

const int kMaxA = 201718;
const int kMaxJump = 20;
const int kMaxN = 1000000;

vector<int> c(kMaxA + kMaxJump + 1);

int main() {
  assert(1 << kMaxJump >= kMaxN);
  int n;
  scanf("%d", &n);
  while (n--) {
    int a;
    scanf("%d", &a);
    ++c[a];
  }
  for (int i = 1; i < c.size(); ++i) {
    c[i] += c[i - 1] / 2;
    c[i - 1] %= 2;
  }
  int b = c.size() - 1;
  while (c[b] == 0) --b;
  printf("%d\n", b);
  return 0;
}