// Theta(n*n*log(n))
#include<cstdlib>
#include<cstdio>
#include<ctime>
const int MAXN=810;
int n,v[MAXN],sol;
void read()
{
	FILE *fin=fopen("nrtri.in","r");
	fscanf(fin,"%d",&n);
	for (int i=1; i<=n; ++i)
		fscanf(fin,"%d",&v[i]);
	fclose(fin);
}
int random(int low,int high)
{
	int r=rand()%(high-low+1);
	return (r+low);
}
void qSort(int low,int high)
{
	int min=low,max=high,mid=random(low,high),temp;
	while (min<=max)
	{
		while (v[min]<v[mid])	++min;
		while (v[max]>v[mid])	--max;
		if (min<=max)
		{
			temp=v[min];
			v[min++]=v[max];
			v[max--]=temp;
		}
	}
	if (min<high)	qSort(min,high);
	if (low<max)	qSort(low,max);
}
int binary_search(int low,int high, int value)
{
	int mid;
	while (low<=high)
	{
		mid=(low+high)/2;
		if (v[mid]<=value)
		{
			int aux=mid+1;
			while (v[aux]<=value && aux<=n)
				++aux;
			return aux-1;
		}
		else if (v[mid]>value)
			high=mid-1;
	}
	return 0;
}
void solve()
{
	int i,j,k=0;
	for (i=1; i<=n-2; ++i)
	{
		for (j=i+1; j<=n-1; ++j)
		{
			k=binary_search(j+1,n,v[i]+v[j]);
			if (k)
			{
				sol+=(k-j);
			}
		}
	}
}
void write()
{
	FILE *fout=fopen("nrtri.out","w");
	fprintf(fout,"%d\n",sol);
	fclose(fout);
}

int main()
{
	srand(time(NULL));
	read();
	qSort(1,n);
	solve();
	write();
	return 0;
}