#include <bits/stdc++.h>
using namespace std;
 
typedef long long  ll;
 
int main() {
 
    int n;
    cin>>n;
 
 
    vector <int> ar;
    for(int i=0;i<=n-1;i++){
    	int y;cin>>y; 
    	ar.push_back(y); 
    }
 
    ll target ;
    cin>>target;
ll count =0;
unordered_map<ll,ll>mpp;
 
for(int j=0;j<n;j++){
	ll rem = target+ar[j];
 
	if(mpp.find(rem)!=mpp.end())
	count+=mpp[rem];
 
	mpp[ar[j]]++;
}
cout<<count;
 
	// your code goes here
	return 0;
}

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5
10 5 7 3 8
2