#include<fstream>
#include<algorithm>
using namespace std;
ifstream in("nrtri.in");
ofstream out("nrtri.out");
int a[100];
int main()
{
	int n,nr=0,i,j,s;
	in>>n;
	for(i=1;i<=n;i++) in>>a[i];
	sort(a+1,a+1+n);
	for(i=1;i<=n;i++)
		for(j=1;j<=n;j++)
		{
			dr=j;
			s=a[i]+a[j];
			while(dr<=n)
			{
				dr++;
				if (s<n) break;
				nr++
			}
		}
	out<<nr;
	return 0;
}