import java.io.*;
import java.util.*;

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
        int a = Integer.parseInt(bf.readLine());
        HashSet<Integer> ka=new HashSet<>();
        String[] s = bf.readLine().split(" ");
        int[] k=new int[a];
        for(int i=0; i<a; i++){
            k[i]=Integer.parseInt(s[i]);
            ka.add(k[i]);
        }
        long p=0;
        for(int i=0; i<a; i++) if(ka.contains(2*k[i]+1)) p++;
        System.out.println(p);
    }
}