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Cod sursa(job #887381)
#include <algorithm>
#include <fstream>
using namespace std;
ifstream fin("oite.in");
ofstream fout("oite.out");
const int mod= (1<<22)-1;
const int nmax= 1024;
int v[nmax+1];
int h[mod+1];
int main(){
int n, s;
fin>>n>>s;
for (int i= 1; i<=n; ++i){
fin>>v[i];
}
sort(v+1, v+n+1);
for (int i= 3; i<n; ++i){
for (int j= i+1; j<=n; ++j){
++h[(v[i]+v[j])&mod];
}
}
int sol= 0;
for (int i= 2; i+2<=n; ++i){
for (int j= 1; j<i; ++j){
sol+= h[(s-v[i]-v[j])&mod];
}
for (int j= i+2; j<=n; ++j){
--h[(v[i+1]+v[j])&mod];
}
}
fout<<sol<<"\n";
return 0;
}