// かいせつ、かしこい

#ifdef LOCAL
    #define _GLIBCXX_DEBUG
    #define __clock__
#else
    #pragma GCC optimize("Ofast")
#endif
#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using VI = vector<ll>;
using VV = vector<VI>;
using VS = vector<string>;
using PII = pair<ll, ll>;

#define UNEXPECTED() cerr << "Unexpected@" << __LINE__ << "!" << endl; exit(1);

// #define INT128 // 必要なら有効化してください
#ifdef INT128
  using LL = __int128;
#endif

// tourist set
template <typename A, typename B>
string to_string(pair<A, B> p);

template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);

template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);

string to_string(const string& s) {
  return '"' + s + '"';
}

string to_string(const char* s) {
  return to_string((string) s);
}

string to_string(bool b) {
  return (b ? "true" : "false");
}

string to_string(char c){
  string s = {c};
  return s;
}

// LL
#ifdef INT128
// input
istream& operator>>(istream& is, LL& v)
{
    string s;
    is >> s;
    v = 0;
    for (int i = 0; i < (int)s.size(); i++) {
        if (isdigit(s[i])) { v = v * 10 + s[i] - '0'; }
    }
    if (s[0] == '-') { v *= -1; }
    return is;
}
std::ostream &operator<<(std::ostream &dest, LL value) {
  std::ostream::sentry s(dest);
  if (s) {
    LL tmp = value < 0 ? -value : value;
    char buffer[128];
    char *d = std::end(buffer);
    do {
      --d;
      *d = "0123456789"[tmp % 10];
      tmp /= 10;
    } while (tmp != 0);
    if (value < 0) {
      --d;
      *d = '-';
    }
    int len = std::end(buffer) - d;
    if (dest.rdbuf()->sputn(d, len) != len) {
      dest.setstate(std::ios_base::badbit);
    }
  }
  return dest;
}
string to_string(LL v){
  stringstream ss;
  ss << v;
  return ss.str();
}
#endif // LL

string to_string(vector<bool> v) {
  bool first = true;
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(v[i]);
  }
  res += "}";
  return res;
}

template <size_t N>
string to_string(bitset<N> v) {
  string res = "";
  for (size_t i = 0; i < N; i++) {
    res += static_cast<char>('0' + v[i]);
  }
  return res;
}

template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}

template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}

template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ")";
}

template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}

void debug_out() { cerr << '\n'; }

template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}

#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif
// tourist set end

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }

#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define rep(i,b) FOR(i, 0, b)
#define ALL(v) (v).begin(), (v).end()
#define p(s) cout<<(s)<<'\n'
#define p2(s, t) cout << (s) << " " << (t) << '\n'
#define SZ(x) ((int)(x).size())
#define SORT(A) sort(ALL(A))
#define RSORT(A) sort(ALL(A), greater<ll>())

#define p_yes() p("Yes")
#define p_no() p("No")
#define p_possible() p("Possible")
#define p_impossible() p("Impossible")
void yes(){p_yes(); exit(0);}
void no(){p_no(); exit(0);}
void possible(){p_possible(); exit(0);}
void impossible(){p_impossible(); exit(0);}

ll SUM(VI& V){
  return accumulate(ALL(V), 0LL);
}

ll MIN(VI& V){return *min_element(ALL(V));}
ll MAX(VI& V){return *max_element(ALL(V));}

void print_vector(VI& V, ll offset=0){
  ll n = V.size();
  rep(i, n){
    if(i) cout << ' ';
    cout << V[i]+offset;
  }
  cout << endl;
}

ll gcd(ll a,ll b){
    if(b == 0) return a;
    return gcd(b,a%b);
}

ll lcm(ll a,ll b){
    ll g = gcd(a,b);
    return a / g * b;
}

// long double
using ld = long double;
// #define EPS (1e-14)
constexpr ld EPS = 1e-14;
// #define equals(a,b) (fabs((a)-(b)) < EPS)
constexpr bool equals(ld a, ld b){return fabs((a)-(b)) < EPS;}

// 小さい順に取り出すpriority queue
using inverse_priority_queue = priority_queue<ll, vector<ll>, greater<ll> >;

int popcount(ll t){
    return __builtin_popcountll(t);
}

// const ll mod = 1e9 + 7;
const ll mod = 998244353;
const ll inf = 4e18; // LLONG_MAX = 9223372036854775807 (atcoder, codeforces)
const double PI = acos(-1);

// [a/b] (繰り上げ)
ll ceil_div(ll a, ll b){
  return (a+b-1)/b;
}

// 累乗※modなし
ll ll_pow(ll a, ll n){
  ll ans = 1;
  rep(i,n){
    ans *= a;
  }
  return ans;
}

// snuke's mint
// auto mod int
// https://youtu.be/L8grWxBlIZ4?t=9858
// https://youtu.be/ERZuLAxZffQ?t=4807 : optimize
// https://youtu.be/8uowVvQ_-Mo?t=1329 : division
// const int mod = 1000000007;
struct mint {
  ll x; // using ll = long long;
  mint(ll x=0):x((x%mod+mod)%mod){}
  mint operator-() const { return mint(-x);}
  mint& operator+=(const mint a) {
    if ((x += a.x) >= mod) x -= mod;
    return *this;
  }
  mint& operator-=(const mint a) {
    if ((x += mod-a.x) >= mod) x -= mod;
    return *this;
  }
  mint& operator*=(const mint a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint a) const {
    mint res(*this);
    return res+=a;
  }
  mint operator-(const mint a) const {
    mint res(*this);
    return res-=a;
  }
  mint operator*(const mint a) const {
    mint res(*this);
    return res*=a;
  }
  mint pow(ll t) const {
    if (!t) return 1;
    mint a = pow(t>>1);
    a *= a;
    if (t&1) a *= *this;
    return a;
  }

  // for prime mod
  mint inv() const {
    return pow(mod-2);
  }
  mint& operator/=(const mint a) {
    return (*this) *= a.inv();
  }
  mint operator/(const mint a) const {
    mint res(*this);
    return res/=a;
  }
};

// ※双方向
// N : 頂点数
// M : 辺数
// return vector<vector<ll>>
VV load_graph(ll N, ll M){
  VV G(N);
  rep(i,M){
    ll a,b;cin>>a>>b;
    a--;b--;
    G[a].push_back(b);
    G[b].push_back(a);
  }
  return G;
}
VV load_tree(ll N){
  return load_graph(N, N-1);
}

VI loadV(ll N){
  VI A(N);
  rep(i,N)cin>>A[i];
  return A;
}

int dx[4] = {-1, 0, 1,  0};
int dy[4] = { 0, 1, 0, -1};

// bool in_range(ll i, ll j){
//   if(0<=i && i<H && 0<=j && j<W){
//     return true;
//   }else{
//     return false;
//   }
// }

//#include <atcoder/dsu>
//using namespace atcoder; // 忘れがち

// for codeforces
void solve(){
  ll N;
  cin>>N;
  VI A(N);
  rep(i, N){
    cin >> A[i];
  }
}

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    // input
    ll N;
    cin>>N;

    VI A(N);
    rep(i, N){
      cin >> A[i];
    }
    RSORT(A);
    
    set<ll> se; // cups
    for(ll a : A){
      auto it = se.lower_bound(a+2);
      if(it==se.end()){
        se.insert(a);
      }
      else{
        se.erase(it);
        se.insert(a);
      }
    }
    p(se.size());

    return 0;
}