#include <iostream>
#include <cmath>
#include<vector>
#include <algorithm>
using namespace std;

int N = 201719;
int* t = new int[N];
int curr_i = 0;
int max_idx = 0;
int maxI = 0;

void shift(int* t) {
  for (int i = 0; i <= max_idx; i++) {
    t[i] = t[i+1];
  }
}

void add(int a) {
  int i = a - curr_i;
  max_idx = max(i, max_idx);
  int v = t[i];
  if(v == 0) {
    t[i] = 1;
    maxI = max(maxI, i+curr_i);
  } else if (v == 1) {
    t[i] = 0;
    add(a+1);
  }
}

int main(int argc, const char* argv[]) {
  size_t n;
  cin >> n;

  std::vector<int> vs (n);

  for(int i = 0; i < n; i++ ) {
    string a;
    cin >> a;
    vs[i] = stoi(a);
  }

  std::sort(vs.begin(), vs.end());

  for(auto v : vs) {
    if(curr_i < v) {
      shift(t);
      curr_i = v;
    }
    add(v);
  }


  cout << maxI << endl;
}