#include <iostream>
#include<bits/stdc++.h>
using namespace std;
 
 
int main() {
	// your code goes here
	int n;
	cin>>n;
	vector<int>arr(n);
	for(int i=0;i<n;i++){
		cin>>arr[i];
	}
	int k;
	cin>>k;
	unordered_map<int,int>mpp;//el,respective count
    int ans=0;
    for(int el:arr){
        if(mpp.find(el+k)!=mpp.end())ans+=mpp[el+k];
        if(mpp.find(el-k)!=mpp.end())ans+=mpp[el-k];
        mpp[el]++;
    }
    cout<<ans;
	return 0;
}

I2luY2x1ZGUgPGlvc3RyZWFtPgojaW5jbHVkZTxiaXRzL3N0ZGMrKy5oPgp1c2luZyBuYW1lc3BhY2Ugc3RkOwoKCmludCBtYWluKCkgewoJLy8geW91ciBjb2RlIGdvZXMgaGVyZQoJaW50IG47CgljaW4+Pm47Cgl2ZWN0b3I8aW50PmFycihuKTsKCWZvcihpbnQgaT0wO2k8bjtpKyspewoJCWNpbj4+YXJyW2ldOwoJfQoJaW50IGs7CgljaW4+Pms7Cgl1bm9yZGVyZWRfbWFwPGludCxpbnQ+bXBwOy8vZWwscmVzcGVjdGl2ZSBjb3VudAogICAgaW50IGFucz0wOwogICAgZm9yKGludCBlbDphcnIpewogICAgICAgIGlmKG1wcC5maW5kKGVsK2spIT1tcHAuZW5kKCkpYW5zKz1tcHBbZWwra107CiAgICAgICAgaWYobXBwLmZpbmQoZWwtaykhPW1wcC5lbmQoKSlhbnMrPW1wcFtlbC1rXTsKICAgICAgICBtcHBbZWxdKys7CiAgICB9CiAgICBjb3V0PDxhbnM7CglyZXR1cm4gMDsKfQ==

NAoxIDIgMiAxCjE=

4
1 2 2 1
1