#include <bits/stdc++.h>
using namespace std;
int main() {
int k;cin>>k;
int n; cin>>n;
int f=0;
unordered_map<int,int> mp;
for(int i=0;i<n;i++){
int t; cin>>t;
if(mp.count(t+k)) f+=(mp[t+k]);
mp[t]++;
}
cout<<f;
}
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