[백준] 1940번 주몽

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

public class Main {
    public static void main(String[] args) {
    	Scanner kb = new Scanner(System.in);
    	
    	int n = kb.nextInt();
    	int m = kb.nextInt();
    	
    	int[] arr = new int[n];
    	
    	for(int i=0; i<n; i++) {
    		arr[i] = kb.nextInt();
    	}
    	
    	Arrays.sort(arr);
    	
    	int lt = 0;
    	int rt = n-1;
    	int count = 0;
    	
    	while(lt<rt) {
    		if(arr[lt]+arr[rt]>m) {
    			rt--;
    		}else if(arr[lt]+ arr[rt]<m) {
    			lt++;
    		}else {
    			count++;
    			lt++;
    			rt--;
    		}
    	}
    	
    	System.out.println(count);
    	
    	
    }
}