BOJ3273.java

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.StringTokenizer;

public class BOJ3273 {
    public static void main(String[] args) throws IOException {
        BufferedReader br= new BufferedReader(new InputStreamReader(System.in));
        int n = Integer.parseInt(br.readLine());
        int[] arr = new int[n];
        StringTokenizer st = new StringTokenizer(br.readLine());
        for(int i=0; i<n; i++)
            arr[i] = Integer.parseInt(st.nextToken());
        int x= Integer.parseInt(br.readLine());
        Arrays.sort(arr);
        int s=0;
        int e=n-1;
        int answer=0;
        while (s<e){
            int sum=arr[s]+arr[e];
            if (sum==x){
                answer+=1;
                s++;
                continue;
            }
            else if(sum<x) s++;
            else e--;

        }
        System.out.println(answer);

    }
}