#include <bits/stdc++.h>
using namespace std;
 
typedef long long int ll;
 
int main() {
    int n;
    cin >> n;
 
    vector<ll> A(n);
    for (int i = 0; i < n; i++) {
        cin >> A[i];
    }
 
    ll target;
    cin >> target;
 
    ll count =0;
   
   unordered_map<ll, ll> mpp;
   
   for(int j=0;j<n ;j++){
   	ll r1= target - A[j];
   	ll r2= -1*target - A[j];
   	
   	if(target==0)
   	count+=mpp[r1];
   	
   	else{
   		count+= mpp[r1];
   		count+= mpp[r2];
   	}
   	
   	mpp[A[j]]++;
   	
   }
   cout<<count<<endl;
 
    return 0;
}