import java.util.Scanner;

public class Main{
	public static void main(String[] args){
		new Main().run();
	}
	//相鄰數對
	public void run(){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		//輸入n個整數，存入陣列
		int[] arr = new int[n];
		for(int i = 0;i < n;i++){
			arr[i] = sc.nextInt();
		}
		
		//比較
		int count = 0;
		for(int j = 0;j < arr.length;j++){
			for(int k = 0;k < arr.length;k++){
				if((arr[j]+1) == arr[k] || (arr[j]-1)==arr[k]){
					count ++;
				}
			}
		}
		if(count > 1){
			count = count/2;
		}
		System.out.println(count);
	}
}