import java.util.Arrays;
import java.util.Scanner;

public class HelloWorld {

	    public static void main(String[] args) throws Exception {

	    	Scanner sc = new Scanner(System.in);
	    	int n = sc.nextInt();
	    	int[] ai = new int[n];
	    	for (int i = 0; i < n; i ++) {
	    		ai[i] = sc.nextInt();
	    	}
	    	sc.close();

	    	Arrays.sort(ai);
	    	int count = 0;
	    	for (int i = n - 1; i >= 1; i --) {
	    		int size_now = 0;
	    		if (ai[i] == 0) {
	    			i --;
	    		}else {
	    			size_now = ai[i];
	    			ai[i] = 0;
	    			count ++;
	    		}


	    		for (int j = i - 1; j >=0; j --) {
	    			if (ai[j] == 0 ) {
		    			j --;
		    		}else if(size_now - 1 > ai[j]){
		    			size_now = ai[j];
		    			ai[j] = 0;
		    		}
	    		}

	    	}

	    	if (ai[0] != 0) {
	    		count ++;
	    	}


	    	System.out.println(count);
	    	}

	    }