#include <fstream>
#define nmax 9000
#define valmax 7000
#pragma GCC optimize("Ofast")

using namespace std;

int v[nmax + 1], f[valmax + 1], mod2[nmax + 1];

int main()
{
    ifstream cin ("medie.in");
    ofstream cout ("medie.out");
    int n, i, j, tot = 0;
    cin >> n;
    for (i = 1; i <= n; i++)
        cin >> v[i], f[v[i]]++, mod2[i] = v[i] % 2;
    for (i = 2; i <= n; i++)
        for (j = i - 1; j >= 1; j--)
            if (mod2[i] == mod2[j])
                tot += f[ (v[i] + v[j]) / 2] - 2 * (v[i] == v[j]);
    cout << tot;
    return 0;
}