#include <cstdio>
#include <algorithm>

using namespace std;

int n,v[1000];

int upper_bd(int l, int r, int x)
{
    int mid,rs=n;
    while(l<=r)
    {
        mid = l + (r-l)/2;
        if(v[mid] < x) l = mid + 1;
        else if(v[mid] > x)
        {
            r = mid - 1;
        }
        else
        {
            rs = mid;
            l = mid + 1;

        }
    }

    return r;
}

int main()
{
    int i,j,poz,sol=0;
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);

    scanf("%d",&n);
    for(i=0;i<n;i++)
        scanf("%d",v+i);

    sort(v,v+n);
    //printf("%d\n",upper_bd(1,n,4));

    for(i=0;i<n-1;i++)
        for(j=i+1;j<n;j++)
        {
            poz = upper_bd(j+1,n-1,v[i]+v[j]);
            if(poz < n)
                sol += poz - j;
        }

    printf("%d",sol);
}