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#include <cstdio>

int acc[210000];

int main() {
  int n;
  scanf("%d", &n);

  int max = 0;
  for (int i = 0; i < n; i++) {
    int a;
    scanf("%d", &a);

    if (max < a) {
      max = a;
    }

    acc[a]++;
  }

  int res = 0;
  for (int i = 0; i < max + 32; i++) {
    if (acc[i] > 1) {
      acc[i + 1] += (acc[i] / 2);
      acc[i] %= 2;
    }

    if (acc[i] > 0) {
      res = i;
    }
  }

  printf("%d\n", res);

  return 0;
}