#include <bits/stdc++.h>
using namespace std;
 
int ans(vector<int> &v,int &k){
	unordered_map<int,int>m;
	int count=0;
	for(int i=0;i<v.size();i++){
		int c=k+v[i];int c1=v[i]-k;
		if(m.find(c)!=m.end()){
			count+=m[c];
		}
		if(k!=0 && (m.find(c1)!=m.end()))count+=m[c1];
		m[v[i]]++;
	}
	return count;
}
int main() {
	// your code goes here
	int n;cin>>n;
	vector<int>v(n);
	for(int i=0;i<n;i++)cin>>v[i];
	int k;cin>>k;
	cout<<ans(v,k)<<endl;
	return 0;
}

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