#include<stdio.h>
#include<algorithm>

using namespace std;

int rez,last,mid,l1,l2,v[1001],i,j,n,s;

int main()
{
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);
    scanf("%d",&n);
    for(i=1;i<=n;i++)
        scanf("%d",&v[i]);
    sort(v+1,v+1+n);
    for(i=1;i<=n-2;i++)
        for(j=i+1;j<=n-1;j++)
        {
            l1=1;
            l2=n;
            s=v[i]+v[j];
            while(l1<=l2)
            {
                mid=(l1+l2)/2;
                if(v[mid]<=s)
                {
                    l1=mid+1;
                }
                else
                    l2=mid-1;

            
            }
            
            rez+=l2-j;;
        }
   printf("%d",rez);
   return 0;
}