#include <fstream>
#include <iostream>
using namespace std;

int n;
int a[9001];

void read() {
    int i;
    ifstream f("medie.in");
    f >> n;
    for (i = 1; i <= n; i++)
        f >> a[i];
    f.close();
}

int fr[7001];
int rez;
int medii[7001];

void solve() {
    int i, start, j, aux;
    for (i = 1; i <= n; i++) {
        if (a[i] % 2 == 0)
            start = 2;
        else start = 1;
        for (j = start; j <= 7000; j += 2)
            medii[(a[i] + j) / 2] += fr[j];
        fr[a[i]]++;
    }
    rez = 0;
    for (i = 1; i <= n; i++) 
        rez += medii[a[i]] - (fr[a[i]] - 1);
}


void output() {
    ofstream g("medie.out");
    g << rez;
    g.close();
}

int main() {
    read();
    solve();
    output();
    return 0;
}