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();
        }
        
                 int compteur = 0;

         int i;

         for (i = 0; i < a.length; i++){
           for(int j = i+1; j < a.length; j++){

             if (Math.abs(a[i] - a[j]) <= 1){
                compteur++;
                break;
             }

           }
         }


         System.out.println(compteur);
    }
}