var f,g : text;
    a : array[1..800] of integer;
    i,j,k,n : integer;
    s,nrs,aux : longint;
    ok : boolean;
begin
assign(f,'nrtri.in'); reset(f);
assign(g,'nrtri.out'); rewrite(g);
readln(f,n);
for i:=1 to n do read(f,a[i]);
repeat
ok:=true;
for i:=1 to n-1 do begin
 if a[i]>a[i+1] then begin
 aux:=a[i];
 a[i]:=a[i+1];
 a[i+1]:=aux;
 ok:=false;
 end;
end;
until ok;

for i:=1 to n-1 do begin
k:=n;
    for j:=n-1 downto i+1 do begin
    s:=a[i]+a[j];
    while (s<a[k]) and (k>0) do dec(k);
    nrs:=nrs+k-j;
                             end;
                   end;
writeln(g,nrs);
close(g);
end.