#include<cstdio>

int n;
int x[801];
long nr = 0;
int s;

int main()
{
	FILE*f;
	
	f = fopen("nrtri.in","r");
	fscanf(f,"%d",&n);
	for (int i=1;i<=n;i++)
		fscanf(f,"%d",&x[i]);
	
	fclose(f);
	
	for (int i=1;i<=(n-2);i++)
		for (int j=(i+1);j<=(n-1);j++)
		{
			s = x[i]+x[j];
			for (int k=(j+1);k<=n;k++)
				if ( s>=x[k] ) nr++; 
				else k++;
		}
	
	f = fopen("nrtri.out","w");
	fprintf(f,"%ld",nr);
	fclose(f);
	
	return 0;
}