#include<cstdio>
#include<algorithm>
using namespace std;
int n,i,j,p,q,nr,st,dr,m,v[805],sol,x;
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+n+1);
    for (i=1;i<n-1;i++)
    for (j=i+1;j<n;j++)
    {
        st=1; dr=n; x=j;
        while (st<=dr)
        {
            m=(st+dr)/2;
            if (v[m]<v[i]+v[j]) st=m+1,x=max(x,m);
            if (v[m]>v[i]+v[j]) dr=m-1;
            if (v[m]==v[i]+v[j]) {x=m; break;}
        }
        sol=sol+x-j;
    }
    printf("%d",sol);
    return 0;
}