#include <stdio.h>
#include <algorithm>
using namespace std;
FILE *fin ,*fout;
bool sortare(int a ,int b)
{
    if(a<=b)return true;
    else return false;
}
int v[801];
int cnt[60001];
int main()
{
    int total=0 , i , j ,n ,k;
    fin=fopen("nrtri.in" ,"r");
    fout=fopen("nrtri.out" ,"w");
    fscanf(fin ,"%d" , &n);
    for(i=1;i<=n;i++)
    {
        fscanf(fin ,"%d" ,&v[i]);
    }
    sort(v+1 ,v+n+1 ,sortare);
    for(i=1;i<n;i++)
    {
        for(j=i+1;j<=n;j++)
        {
            k = j + 1;
            while (k <= n && v[i] + v[j] >= v[k]) k++;
            total=total + k-j-1;

        }
    }
    fprintf(fout ,"%d" ,total);
    return 0;
}