import java.util.*;

public class hackerrank101 {
	public static void main(String args[]){
		 Scanner s= new Scanner(System.in);
	        int n = s.nextInt();
	        
	        int count=0;
	        int[] a = new int[n];
	        int[] b = new int[n];
	        for(int i=0; i < n; i++){
	            a[i] = s.nextInt();
	           }
	        Arrays.sort(a);
	        for(int k=0;k<n-1;k++){
	        	if(a[k+1]-a[k]<=1){
	        		count++;
	        	}
	        }
	    System.out.println(count);
}
}