#include <fstream>
#include <algorithm>
using namespace std;

ifstream fin("nrtri.in");
ofstream fout("nrtri.out");


long a[801], n, i, j, v, k;
long long nr;
long  mij;
int BS(long val); 

int main()
{
	fin >> n;
	for ( i = 0; i < n; i++)
		fin >> a[i];
	fin.close();
	
	sort(a, a + n);

	for ( i = 0; i < n - 2; i++)
		for ( j = i + 1; j < n - 1; j++)
		      nr +=  BS(a[i]+a[j]) - j;
                
		            
		    
					
				
	fout << nr << '\n';
	fout.close();
	return 0;
}

int BS(long val)
{
    int mij, st = 0, dr = n-1;
    while ( st <= dr)
    {
        mij = (st + dr) / 2;
        if ( (a[mij] <= val && a[mij+1] > val) || (a[mij] <= val && mij == n - 1)) 
                return mij;
        if ( a[mij] <= val ) st = mij + 1;
        if ( a[mij] > val) dr = mij - 1;
    }
    return 0;    
}