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#include <iostream>

const unsigned MAX_EXP = 201719;
unsigned buckets[MAX_EXP];

int main() {
  unsigned n;
  unsigned input;
  scanf("%u", &n);
  for (unsigned i = 0; i < n; i++) {
    scanf("%u", &input);
    buckets[input]++;
  }
  unsigned maxi = 0;
  for (unsigned i = 0; i < MAX_EXP - 1; i++) {
    if (buckets[i] > 0) maxi = i;
    buckets[i + 1] += buckets[i] / 2;
  }
  if (buckets[MAX_EXP - 1] > 0) {
    maxi = MAX_EXP - 1;
    while (buckets[MAX_EXP - 1] > 1) {
      buckets[MAX_EXP - 1] /= 2;
      maxi++;
    }
  }
  printf("%u", maxi);
}