#include<bits/stdc++.h>
//#include <atcoder/all>

#define INF 1e9
#define rep(i,n)for(int i=0;(i)<(int)(n);i++)
#define REP(i,a,b)for(int i=(int)(a);(i)<=(int)(b);i++)
#define ALL(a)  (a).begin(),(a).end()
#define chmax(a, b) a = max(a, b)
#define chmin(a, b) a = min(a, b)
#define pb push_back
#define fi first
#define se second
#define sz(x) ((int)x.size())

using namespace std;
//using namespace atcoder;
using ld = long double;
using ll = long long;
using P = pair<ll, ll>;
using Graph = vector<vector<int>>;

const ll ZER = 0;
const ll MOD = 1e9 + 7;


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

    int n;
    cin >> n;
    vector<ll> a(n);
    rep(i, n)cin >> a[i];
    sort(ALL(a), greater<>());
    queue<ll> q;
    rep(i, n){
        q.push(a[i]);
        if(a[i] + 1 < q.front())q.pop();
    }
    cout << sz(q) << endl;
}