[백준] 3273번 두 수의 합 문제! (silver 3

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));
        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
        int t=Integer.parseInt(br.readLine());
        int[] num=new int[2000001];
        StringTokenizer st=new StringTokenizer(br.readLine());
        for(int i=0; i<t; i++){
            num[Integer.parseInt(st.nextToken())]++;
        }
        int n=Integer.parseInt(br.readLine());
        int total=0;
        for(int i=n/2+1; i<n; i++){
            if(num[i]==1 && num[n-i]==1){
                total++;
            }
        }
        bw.write(total+"");
        bw.flush();

    }

}