var a: array [1..1000] of integer;
i,n,d,t,j : integer;
begin
writeln('Nhap n : ');readln(n);
for i:= 1 to n do begin
writeln;
write('a[',i,'] = ' );
readln(a[i]);
end;
t:=0;
for i:= 1 to n do
begin
d:=0;
for j:= i to n do if a[i]=a[j] then d:=d+1;
t:=t + (d div 2);
if (d>1) and (d mod 2>=1) then t:=t-(d mod 2);
end;
writeln;
writeln(t);
readln
end.