#include<iostream>
#include<map>
#include<vector>
#include <algorithm>
#include<math.h>
#include <iomanip>
#include<set>
#include <numeric>
#include<string>
using namespace std;

int main()
{
    int n;
    cin >> n;
    vector<vector<int>> a(1);
    for (int i = 0; i < n; i++){
        int t;
        cin >> t;
        a[0].push_back(t);
    }
    sort(a[0].begin(), a[0].end());
    for (int i = 0; i < a.size(); i++){
        for (int j = 0; j < a[i].size() - 1; j++){
            if (a[i][j] + 1 >= a[i][j+1]){
                if (a.size() == i+1) a.push_back({a[i][j+1]});
                else a[i+1].push_back(a[i][j+1]);
                a[i].erase(a[i].begin() + j + 1);
            }   
        }
    }
    
    cout << a.size() << endl;
}