var
  n,i,s,j:longint;
  a:array [0..1000] of longint;
  f:array [0..20000] of boolean;
begin
 // assign(input,'count.in');
  //reset(input);
  //assign(output,'count.out');
 // rewrite(output);
  readln(n);
  for i:=1 to n do    read(a[i]);

 for i:=0 to 20000 do    f[i]:=false;
  for i:=1 to n-1 do
    for j:=i+1 to n do
      f[a[i]+a[j]]:=true;
  s:=0;
  for i:=1 to n do
    if f[a[i]] then
      s:=s+1;
  writeln(s);
  //close(input);
  //close(output);
end.

/**************************************************************
	Problem: 2330
	User: admin
	Language: Pascal
	Result: Wrong Answer
****************************************************************/