#include <stdio.h>
#include <algorithm>
using namespace std;
FILE *fin=fopen("nrtri.in","r");
FILE *fout=fopen("nrtri.out","w");
int n,i,a[802],ind,s,nr,j;

int main()
{
    fscanf(fin,"%d",&n);
    for(i=1;i<=n;i++)fscanf(fin,"%d",&a[i]);
    sort(a+1,a+n+1);
    for(i=1;i<n-1;i++)
        for(j=i+1;j<n;j++)
        {
        s=a[i]+a[j];
        ind=upper_bound(a+1,a+n+1,s)-a;
        if(ind<=n)
        {
            ind --;
            nr+=ind-i-1;
        }
        }
    fprintf(fout,"%d",nr);
    return 0;
}