#include <iostream>
#include <algorithm>
using namespace std;
int n,v[1003];
int cautbin(int a)
{
    int p = 1, u = n, poz = 0;
    while(p <= u)
    {
        int m = (p + u) / 2;
        if(v[m] < a)
        {
            poz = m;
            p = m + 1;
        }
        else
            u = m - 1;
    }
    return poz;
}

int main()
{
    int s=0,p;
    cin>>n;
    for(int i=1;i<=n;i++)
        cin>>v[i];
    sort(v+1,v+n+1);
    for(int i=1;i<n;i++)
        for(int j=i+1;j<=n;j++)
        {
            p=cautbin(v[i]+v[j]);
            s+=p-j;
        }
    cout<<s;
    return 0;
}