#include<cstdio>
#include<algorithm>
using namespace std;
int p,u,mij,ras,ras1,xx,nr,i,j,ij,n,a[801];
int main()
{
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);
    scanf("%d",&n);
    for(i=1;i<=n;i++)
    {
        scanf("%d",&a[i]);
    }
    sort(a+1,a+1+n);
    for(i=1;i<=n-1;i++)
    {
        for(j=i+1;j<=n;j++)
        {
            p=1;
            u=n;
            ras=ras1=n;
            while(p<=u)
            {
                mij=(p+u)/2;
                if(a[mij]<=a[i]+a[j])
                {
                    ras=mij;
                    p=mij+1;
                }
                else u=mij-1;
            }
            p=1;
            u=n;
            xx=a[i]-a[j];
            if(xx<0) xx=xx*(-1);
            while(p<=u)
            {
                mij=(p+u)/2;
                if(a[mij]<xx)
                {
                    ras1=mij;
                    p=mij+1;
                }
                else u=mij-1;
            }
            nr=nr+ras-ras1;
        }
    }
    printf("%d",nr/2);
    return 0;
}