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

public class Solution {
    
    public static int abs(int a) {
        return (a <= 0) ? 0 - a : a;
    }
    
    public static void findDiff(int[] ar) {
        Arrays.sort(ar); 
        int count=0;
        for(int i=1; i<ar.length;i++){
            if(abs(ar[i] - ar[i-1]) <=1){
                count++;
            }
            
        }
        System.out.print(count);
        
    } // findDiff
    

    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();
        }
        findDiff(a);
    }
}