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#include<cstdio>

const int N = 300000;
int bits[N];
int n;
int* t;
int solution;

void input() {
  scanf("%d", &n);
  t = new int[n];
  for (int i = 0; i < n; i++) {
    scanf("%d", t + i);
  }
}

void setBits() {
  for (int i = 0; i < n; i++) {
    bits[t[i]]++;
  }
}

void carry() {
  int carryOver = 0;
  for (int i = 0; i < N; i++) {
    carryOver += bits[i];
    bits[i] = carryOver % 2;
    carryOver /= 2;
  }
}

void findSolution() {
  for (int i = N - 1; i >= 0; i--) {
    if (bits[i] != 0) {
      solution = i;
      return;
    }
  }
}

void solve() {
  setBits();
  carry();
  findSolution();
}

void printSolution() {
  printf("%d\n", solution);
}

int main(int argc, char ** argv) {
  input();
  solve();
  printSolution();
}