var v:array[1..800] of longint;
    f,g:text;
    i,j,aux,p,n,dr,st,tg,mij:longint;
begin
assign(f,'nrtri.in');reset(f);
assign(g,'nrtri.out');rewrite(g);
readln(f,n);
for i:=1 to n do
    read(f,v[i]);
for i:=1 to n-1 do
    for j:=i+1 to n do
       if v[i]>v[j] then
           begin
            aux:=v[i];
            v[i]:=v[j];
            v[j]:=aux;
           end;
for i:=1 to n-1  do
    for j:=i+1 to n do
       begin
         st:=j;
         dr:=n+1;
         tg:=v[i]+v[j];
         while ((dr-st)>1) do
           begin
             mij:=(st+dr) div 2;
             write(g,'st=',st,' ','dr=',dr,' ','mij=',mij,' ');
             if v[mij]<tg then st:=mij
                           else dr:=mij;
           end;
         p:=p+mij-(j);
         write(g,'p=',p,' ');
       end;
write(g,p);
close(f);
close(g);
end.