type vect = array[1..800] of integer;

var fi,fo:text;
    i,j,n,x,y,z,mj,st,dr:integer;
    a:vect;
    ntri:longint;

 procedure heapsort(n:integer);
  var aux,k:integer;
  begin
   for i:=1 to n do
    begin
     j:=i;
     while (j div 2<>0) and (a[j div 2]<a[j]) do
      begin
        aux:=a[j div 2];
        a[j div 2]:=a[j];
        a[j]:=aux;
        j:=j div 2;
      end;
    end;
   i:=n;
   while i>1 do
    begin
     aux:=a[1];
     a[1]:=a[i];
     a[i]:=aux;
     dec(i);
     j:=1;
     while (1>0) do
      begin
       k:=2*j;
       if (k>i) then  break;
       if (k+1<=i) and (a[k+1]>a[k]) then inc(k);
       if a[j]>=a[k] then break;

       aux:=a[j];
       a[j]:=a[k];
       a[k]:=aux;
       j:=k;
      end;
     end;
  end;





begin
 ntri:=0;
 assign(fi,'nrtri.in'); reset(fi);
 assign(fo,'nrtri.out'); rewrite(fo);
 readln(fi,n);
 for  i:=1 to n do   read(fi,a[i]);
 heapsort(n);
 for i:=1 to n-2 do
  for j:=i+1 to n-1 do
   begin
    x:=a[i];
    y:=a[j];
    st:=j+1;
    dr:=n;
    z:=x+y;
    if z>=a[n] then begin mj:=n; inc(ntri,n-j); continue; end;
    while st<=dr do
     begin
      mj:=(st+dr) div 2;
      if z<a[mj] then dr:=mj-1;
      if z>a[mj] then st:=mj+1;
      if z=a[mj] then break;
     end;
    if   z<a[mj] then
     dec(mj);
    if mj+1<=n then
     if z>a[mj+1] then inc(mj);
    if a[mj]=z then
     begin
      while a[mj]=z do
       inc(mj);
      dec(mj);
     end;
     if mj+1<=n then
      if z>a[mj+1] then inc(mj);
     if a[mj]=z then
     begin
      while a[mj]=z do
       inc(mj);
      dec(mj);
     end;
    if (mj=j+1) then if (z<a[mj]) then mj:=j;
    ntri:=ntri+mj-j;
  end;
writeln(fo,ntri);
close(fo);
end.