#include<cstdio>
#include<algorithm>

using namespace std;

int i,j,n,a[10002],ans=0;

int bin(int x,int st)
{
    int dr=n,mij;
    while(st<=dr)
    {
        mij=(st+dr)/2;
        if(a[mij]<=x&&(a[mij+1]>x||mij==n))
        {
            return mij;
        }
        else
        {
            if(a[mij]<=x)
            {
                st=mij+1;
            }
            else
            {
                dr=mij-1;
            }
        }
    }
    return j;
}

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);
    for(i=1;i<n-1;i++)
    {
        for(j=i+1;j<n;j++)
        {
            ans+=bin(a[i]+a[j],j)-j;
        }
    }
    printf("%d\n",ans);
}