#include<stdio.h>
#include<algorithm>
using namespace std;
FILE *in,*out;
int i,n,v[800],j,k,nr;
int main()
{
    in=fopen("nrtri.in","rt");
    out=fopen("nrtri.out","wt");
    fscanf(in,"%d",&n);
    for(i=1;i<=n;i++)
        fscanf(in,"%d",&v[i]);
    sort(v+1,v+n+1);
    for(i=1;i<=n-2;i++)
        for(j=i+1;j<=n-1;j++)
        {
            k=j+1;
            while((v[i]+v[j])>=v[k] && k<=n)
                k++;
            nr+=k-1-j;
        }
    fprintf(out,"%d",nr);
}