#include <bits/stdc++.h>

using namespace std;

ifstream fin("medie.in");
ofstream fout("medie.out");

int n, v[9005], fr[7005];
vector <int> pos[7005];
long long ans;

int gasit(int val, int i)
{
    int st = 0, dr = pos[val].size() - 1;
    while (st <= dr)
    {
        int mid = (st + dr) / 2;
        if (pos[val][mid] == i) return 1;
        else if (pos[val][mid] > i) dr = mid - 1;
        else st = mid + 1;
    }
    return 0;
}

int main()
{
    fin >> n;
    for (int i = 1; i <= n; ++i)
    {
        fin >> v[i];
        fr[v[i]]++;
        pos[v[i]].push_back(i);
    }
    for (int i = 1; i < n; ++i)
        for (int j = i + 1; j <= n; ++j)
        {
            if (v[i] % 2 != v[j] % 2) continue;
            int x = (v[i] + v[j]) / 2;
            ans = ans + fr[x] - gasit(x, i) - gasit(x, j);
        }
    fout << ans;
    fin.close();
    fout.close();
    return 0;
}