#include<stdio.h>
#include<stdlib.h>

int v[30720], val[1024];

int cmp(const void *a, const void *b)
{
	return *(int *)b - *(int *)a;
}


int main()
{
	freopen("nrtri.in", "r", stdin);
	freopen("nrtri.out", "w", stdout);

	int n, i, j, sol=0, sol2=0;
	
	scanf("%d", &n);
	for (i=1; i<=n; i++)
	{
		scanf("%d", &val[i]);
		++v[val[i]];
		//if (v[val[i]]>1) ;
	}
	for (i=1; i<=30000; i++)
		v[i]+=v[i-1];
	
	qsort(val+1, n, sizeof(int), cmp);
		
	for (i=1; i<n-1; i++)
		for (j=i+1; j<n; j++)
			if (val[i]-val[j] <= val[j]) {sol+=v[val[j]] - v[val[i]-val[j]-1]-1; sol2+=v[val[j]-1] - v[val[i]-val[j]-1];}
	
	printf("%d", (sol+sol2)/2);
	return 0;
}