import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int[] a = new int[n];
        for(int a_i=0; a_i < n; a_i++){
            a[a_i] = in.nextInt();
        }
        String s="";

        Arrays.sort(a);
       for(int i=0;i<n-1;i++)
           {
              if(a[i+1]-a[i]<=1)
               {
               s+=a[i]+" ";
                  s+=a[i+1]+" ";
           }
           
       }
      
    String[] res=s.split(" ");
           
        int count=0;
         
        for(int i=0;i<res.length-1;i++)
            {
            if(res[i]==res[i++])
                i++;
            count++;
        }
System.out.println(count);
    }
}