#include <bits/stdc++.h>
#define st first
#define nd second
#define pb push_back
#define NMAX 200005
using namespace std;
typedef long long ll;
FILE *fin=fopen("medie.in","r");
FILE *fout=fopen("medie.out","w");
int n, m, i, j, x, ans, fr[7005];
void fast()
{
    ios_base::sync_with_stdio(false);
    cin.tie();
}
int main()
{
    fast();
   /// cin>>n;
    fscanf(fin,"%d",&n);
    for(i=1;i<=n;++i)
    {
      //  cin>>x;
        fscanf(fin,"%d",&x);
        fr[x]++;
    }
    for(i=1;i<=7000;++i)
        if(fr[i])
    {
        ans+=fr[i]*(fr[i]-1)*(fr[i]-2)/2;
        for(j=1;j<i;++j)
            if(fr[j])
                ans+=fr[j]*fr[i]*fr[2*i-j];
    }
    fprintf(fout,"%d",ans);
    //cout<<ans;
    return 0;
}