#include<fstream>

#define M 801
using namespace std;
ifstream f("nrtri.in");
ofstream g("nrtri.out");
int n,v[M];

void citire()
{

int i=0;
f>>n;
while (++i<=n)
f>>v[i];
}

int compar(const void *p,const void *q)
{
int x=*(int*)p,y=*(int*)q;
if(x<y)
return -1;
if(x>y)
return 1;
return 0;
}

void calcul()
{
int i,j,k,perechi=0;
for(i=1;i<=n-2;++i)
{
k=i+2;
for(j=i+1;j<=n-1;++j)
{
while( k<=n && v[i]+v[j]>=v[k] )
++k;
perechi+=k-j-1;
}
}
g<<perechi;
}

int main()
{
citire();
qsort(v+1,n,sizeof(v[0]),compar);
calcul();
return 0;
}