#include <cstdio>
#include <algorithm>
using namespace std;
int v[2003];

int main()
{
    int i,j,nr,n,c1,c2,mij,apare;
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);
    scanf("%d",&n);
    nr=0;
    for(i=1; i<=n; i++)scanf("%d",&v[i]);
    sort(&v[1],&v[n+1]);
    for(i=1; i<=n-3; i++)
    {
        for(j=i+1; j<=n-1; j++)
        {
            c1=j+1;
            c2=n;
            apare=0;
            while(c1<=c2)
            {
                mij=(c1+c2)/2;
                if(v[mij]<v[i]+v[j])
                {
                    c1=mij+1;

                }
                else if(v[mij]>v[i]+v[j])c2=mij-1;
                else
                {
                    apare=1;
                    break;
                }

            }
            if(apare==0)nr=nr+(c2-j);
            else
            {
                while(v[mij]==v[i]+v[j]&&mij<n)mij++;
                nr=nr+mij-j;
            }

        }
    }

    if(v[n-2]+v[n-1]>v[n])nr++;
    printf("%d",nr);
    return 0;
}