#include<stdio.h>

#define IN "nrtri.in","r",stdin
#define OUT "nrtri.out","w",stdout

int N ;
int V[900] ;
int main()
{
	freopen(IN);
	freopen(OUT);
	scanf("%d",&N);
	int p = 3;
	int perechi = 0;
	for(int i = 1; i <= N ; ++i)	scanf("%d",&V[i]);
	for(int i = 1 ; i <= N - 2; ++i)
		for(int j = i + 1, p = j+1; j <= N-1; ++j)
		{
			for(; p <= N && V[i] + V[j] >= V[p]; ++p);
			perechi += p-1-(j+1)+1;
		}
	printf("%d\n",perechi);
	return 0;
}