#include <fstream>
#define nmax 7010
using namespace std;

int Answer,A[nmax];

void Solve() {

    int i,j;

    for(i=0;i<nmax;i++)
        if(A[i]) {

            for(j=i+2;j<nmax;j+=2)
                if(A[j] && A[(i+j)>>1])
                    Answer+=A[i]*A[j]*A[(i+j)>>1];

            Answer+=A[i]*(A[i]-1)*(A[i]-2)/2;

            }

}
void Read() {

    int i,x,N;
    ifstream in("medie.in");

    in>>N;
    for(i=1;i<=N;i++) {
        in>>x;
        A[x]++;
        }

    in.close();

}
void Write() {

    ofstream out("medie.out");
    out<<Answer<<'\n';
    out.close();

}
int main() {

    Read();
    Solve();
    Write();

    return 0;

}