#include<fstream>
#include<algorithm>
using namespace std;
ifstream f("nrtri.in");
ofstream g("nrtri.out");

int main()
	{
		int v[850],i,j,l,k=0;
		f >> n;
		for(i=1;i<=n;i++)f >> v[i];
        sort(v+1;v+n+1);
		for(i=1;i<=n;i++)
			for(j=i+1;j<=n;j++)
				for(l=j+1;l<=n;l++)
					if(v[i]+v[j]>=v[k])k++;else break;
		g << k;
		return 0;
    }