#include <bits/stdc++.h>

using namespace std;

#define REP(i, n) for (int i=0; i<(n); ++i)
#define FOR(i, a, n) for (int i=(a); i<(n); ++i)

#define SZ(x) ((int)(x).size())
#define ALL(x) (x).begin(),(x).end()

#define DUMP(x) cerr<<#x<<" = "<<(x)<<endl
#define DEBUG(x) cerr<<#x<<" = "<<(x)<<" (L"<<__LINE__<<")"<<endl;

template<class T>
ostream &operator<<(ostream &os, const vector<T> &v) {
  os << "[";
  REP(i, SZ(v)) {
    if (i) os << ", ";
    os << v[i];
  }
  return os << "]";
}

template<class T, class U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
  return os << "(" << p.first << " " << p.second << ")";
}

template<class T>
bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}

template<class T>
bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return true;
  }
  return false;
}

using ll = long long;
using ull = unsigned long long;
using ld = long double;
using P = pair<int, int>;
using vi = vector<int>;
using vll = vector<ll>;
using vvi = vector<vi>;
using vvll = vector<vll>;

const ll MOD = 1e9 + 7;
const int INF = INT_MAX / 2;
const ll LINF = LLONG_MAX / 2;
const ld eps = 1e-9;

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(10);

  int n; cin >> n;
  map<int, int> mp;
  REP(i, n) {
    int a; cin >> a;
    mp[a]++;
  }
  vector<P> v;
  for(auto &e: mp) {
    v.emplace_back(e);
  }

  int ma = 1;
  REP(i, SZ(v)) {
    chmax(ma, v[i].second);
  }
  REP(i, SZ(v)-1) {
    if(v[i].first == v[i+1].first - 1) {
      chmax(ma, v[i].second + v[i+1].second);
    }
  }
  cout << ma << endl;


  return 0;
}