#include <cstdio>
#include<algorithm>
using namespace std;
const int vmax=30000,nmax=800;
int ve[nmax+5];
int main()
{
    freopen("nrtri.in","r",stdin);
    freopen("nrtri.out","w",stdout);
    int n,i,j,st,dr,mi,la,ans=0;
    scanf("%d",&n);
    for(i=1;i<=n;i++)
        scanf("%d",&ve[i]);
    sort(ve+1,ve+n+1);
    for(i=1;i<n;i++)
        for(j=i+1;j<n;j++)
    {
        st=j+1;
        dr=n;
        la=-1;
        while(st<=dr)
        {
            mi=(st+dr)/2;
            if(ve[mi]<=ve[i]+ve[j])
            {
                la=mi;
                st=mi+1;
            }
            else
                dr=mi-1;
        }
        if(la!=-1)
         ans=ans+la-j;
    }
    printf("%d\n",ans);
    return 0;
}