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var
f : text;
i, l, m, n : integer;
a : array[1..1000] of longint;
procedure qsort(l, h : integer);
var
i, j : integer;
x, tmp : longint;
begin
i := l;
j := h;
x := a[(i + j) div 2];
repeat
while a[i] < x do inc(i);
while x < a[j] do dec(j);
if i <= j then
begin
tmp := a[i];
a[i] := a[j];
a[j] := tmp;
inc(i);
dec(j)
end
until i > j;
if l < j then qsort(l, j);
if i < h then qsort(i, h)
end;
function biin(n0 : integer) : boolean;
var l, h, m : integer;
begin
l := 1;
h := n;
repeat
m := (l + h) div 2;
if a[m] = n0 then exit(true);
if a[m] < n0 then l := m + 1
else h := m - 1
until l > h;
biin := false
end;
function libtbc(n0 : integer) : boolean;
var i, j : integer;
begin
for i := 1 to n0 - 1 do
for j := n0 + 1 to n do
if biin(a[n0] * 3 - a[i] - a[j]) then
exit(true);
libtbc := false
end;
begin
assign(f, 'TBC.INP');
reset(f);
readln(f, n);
for i := 1 to n do readln(f, a[i]);
close(f);
qsort(1, n);
m := 0;
for l := 2 to n - 1 do
if libtbc(l) then
inc(m);
assign(f, 'TBC.OUT');
rewrite(f);
writeln(f, m);
close(f)
end.
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