#include <fstream>
#include <algorithm>
#include <cstdio>
using namespace std;
ofstream fout("nrtri.out");
int n,i,s,a[30001],j,*p,poz;
bool test(int x,int y)
{
    return x<y;
}
int main()
{
    freopen("nrtri.in","r",stdin);
    scanf("%d",&n);
    for(i=1;i<=n;i++)
        scanf("%d",&a[i]);
    sort(a+1,a+n+1,test);
    for(i=1;i<=n-2;i++)
        for(j=i+1;j<=n-1;j++)
        {
            p=upper_bound(a+j+1,a+n+1,a[i]+a[j]);
            poz=p-a-1;
            if(poz<=n && poz>=1)
                s=s+poz-j;
        }
    fout<<s<<'\n';
    return 0;
}