uses crt;

type vector=array[1..800] of longint;

var v:vector;
	f,g:text;
	k,j,x,nr,i,n:longint;
	rez:longint;
procedure sort;                 //sortez vectorul crescator cu ajutorul unei variabile auxiliare
var i,j,aux : longint;
begin
	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;
end;

begin
	assign(f,'nrtri.in');
	reset(f);
	assign(g,'nrtri.out');
	rewrite(g);
	read(f,n);
	rez:=0;
	for i:=1 to n do 
		read(f,v[i]);
	sort;
	for i:=1 to n-2 do 
		begin
			k:=i+2;
			for j:=i+1 to n do
				begin
					while (k<=n) and (v[k] <= v[i]+v[j]) do 
						k:=k+1;
					if k>j then rez:=rez+k-j-1;
				end;
		end;
	writeln(g,rez);	
	close(g);
	close(f);
end.