#include <cstdio>
#include <algorithm>
using namespace std;
int n,i,ls,ld,l,poz,s,j,a[1002];
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+n+1);
    a[n+1]=1000000;
    for(i=1;i<=n-2;i++)
    {
        for(j=i+1;j<=n-1;j++)
        {
            ls=j+1;
            ld=n;
            poz=-1;
            while(ls<=ld)
            {
                l=(ls+ld)/2;
                if(a[l]<=a[i]+a[j]&&a[l+1]>a[i]+a[j]){poz=l;break;}
                else
                {
                    if(a[l]>a[i]+a[j])ld=l-1;
                    else if(a[l]<=a[i]+a[j]&&a[l+1]<=a[i]+a[j])ls=l+1;
                }
            }
            if(poz>-1)s=s+poz-j;
        }
    }
    printf("%d",s);
    return 0;
}