#include <fstream>
#include <iostream>

using namespace std;

ifstream inf("medie.in");
ofstream outf("medie.out");

int ap[7001];
int apv[7001];
int v[9000];

int main() {
    int n;
    inf >> n;
    for(int i = 0; i < n; i++) {
        inf >> v[i];
        apv[v[i]]++;
        for(int j = 0; j < i; j++) {
            if(!((v[i] & 1) ^ (v[j] & 1))) {
                ap[((v[i] + v[j]) >> 1)]++;
            }
        }
    }
    long long rez = 0;
    for(int i = 0; i < n; i++) {
        rez += ap[v[i]] - apv[v[i]] + 1;
    }
    outf << rez;
    return 0;
}