#include <fstream>
#include <unordered_map>
using namespace std;
ifstream in("oite.in");
ofstream out("oite.out");
int c, l, v[1024 + 2], comb;
unordered_map <int, int> m;
int main(){
    in>>c>>l; for(int i = 0; i < c; i++) in>>v[i];
    for(int i = 0; i < n; i++){
        for(int j = i + 1; j < n; j++){
            if(f.find(s - v[i] - v[j]) != f.end())
                comb += f[s - v[i] - v[j]];
        }
        for(int j = 0; j < i; j++)
            f[v[i] - v[j]] += 1;
    }
    out<<comb;
    return 0;
}