#include<fstream.h>
int main()
{unsigned v[801], n, a, i, j, ok, aux;
ifstream f("nrtri.in");
ofstream g("nrtri.out");
f>>n;
a=0;
for (i=1; i<=n; i++) f>>v[i];
do {ok=0;
for (i=1; i<=n-1; i++)
if (v[i]>v[i+1]) {aux=v[i]; v[i]=v[i+1]; v[i+1]=aux; ok=1;}
}
while (ok==1);
for (i=1; i<=n/2; i++)
		{ok=1;
		for(j=i+1; j<=n-i&&ok==1; j++)
		     if (v[i]+v[n-i+1]>=v[j]&&v[i]+v[j]>=v[n-i+1]&&v[n-i+1]+v[j]>=v[i]) a++;
		     else ok==0;
        }
g<<a;
f.close();
g.close();
return 0;
}