#include<bits/stdc++.h>
using namespace std;
int n, x, a[1000010],sum=0;
int main(){
	cin >> n;
	for(int i = 0;i < n; i++){
		cin >> a[i];
	}
	cin >> x;
	sort(a, a + n);
	for(int i = 0;i < n; i++){
		int idx = lower_bound(a, a + n, x - a[i]) - a;
		if(a[idx] == x - a[i]) sum++;
	}
	cout << sum / 2;
	return 0;
}