[백준] 1940번 주몽 (silver 4

import java.io.*;
import java.util.*;
public class Main {
	public static void main(String[] args) throws IOException {
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		int n=Integer.parseInt(br.readLine());
		int m=Integer.parseInt(br.readLine());
		StringTokenizer st=new StringTokenizer(br.readLine());
		int[] num=new int[n];
		for(int i=0; i<n; i++){
			num[i]=Integer.parseInt(st.nextToken());
		}
		Arrays.sort(num);
		int answer=0;
		int start=0;
		int end=n-1;
		while(end!=start){
			int temp=num[start]+num[end];
			if(temp==m){
				answer+=1;
				start+=1;	
			}
			else if(temp>m){
				end-=1;
			}
			else{
				start+=1;
			}
		}
		System.out.print(answer);
	}
}