program doKhoangCach;
var a, b, x, y: integer;
khcach, max: real;
t: text;
begin
assign(t,'TRAI.TXT');
reset(t);
read(t,a,b);
khcach := 0;
while not eof(t) do
begin
read(t,x,y);
khcach := sqrt(sqr(a-x)+sqr(b-y));
if khcach > max then max := khcach;
end;
close(t);
assign(t,'KCMAX.OUT');
rewrite(t);
write(t,max:0:5);
close(t);
end.