var n,i,j,k:integer;
    f,g:text;
begin
assign(f,'nrtri.in');reset(f);
assign(g,'nrtri.out');rewrite(g);
read(f,n);
for i:=1 to n do
    read(f,k);
write(g,n div 2);
close(f);
close(g);
end.