#include <iostream>
#include <vector>
using namespace std;
vector<bool> num(2000005, false);
int main() {
int n, x, t, answer = 0;
scanf("%d",& n);
for(int i = 0; i < n; i++) {
scanf("%d", &t);
num[t] = true;
}
scanf("%d", &x);
for(int i = 1; i<= x / 2; i++)
if(num[i] && num[x - i]) answer++;
if(x % 2 == 0 && num[x / 2]) answer--;
printf("%d", answer);
}