#include<stdio.h>
#include<iostream.h>

FILE*fin=fopen("nrtri.in","r");
FILE*fout=fopen("nrtri.out","w");

long n,i,j,v[801],ab,nrtri;

int citire()
{fscanf(fin,"%d",&n);
for(i=1;i<=n;i++) fscanf(fin,"%d",&v[i]);}

int sortare()
{int ad=0,var;
while(ad==0)
{ad=1;
for(i=1;i<n;i++)
if(v[i]>v[i+1])
{ad=0; var=v[i]; v[i]=v[i+1]; v[i+1]=var;}}
}

int binar()
{int test=j+(n-j)/2,k,var=0;
if(v[test]>ab) {for(k=test-1;k>=j+1;k--)
		if(v[k]<=ab) var++;}

else {for(k=test;k>=j+1;k--) var++;
      for(k=test+1;k<=n;k++) if(v[k]<=ab) var++;
			     else break;       }
nrtri+=var;}



main()
{citire(); sortare();

for(i=1;i<=n-2;i++)
for(j=i+1;j<=n-1;j++) {ab=v[i]+v[j]; binar();}

fprintf(fout,"%ld",nrtri); cout<<endl;
}