program bai_giai;
uses crt;
var f,g:text;
A:array[1..10000] of integer;
n,i,j,d:integer;
begin
Assign(f,'BAI2.INP'); reset(f);
Assign(g,'BAI2.OUT'); rewrite(g);
readln(f,n);
for i:=1 to n do read(f,A[i]);
d:=0;
for i:=1 to n-1 do
for j:=i+1 to n do
if (A[i]+A[j]) mod 2=0 then d:=d+1;
write(g,d);
close(f); close(g);
end.