program c;
var x,p,a,y:real;
begin
writeln ('input x,p,a');
readln (x,p,a);
if  (x)<=-p then y:=0
else if (x)>=p then y:=0
else if (0)<x<(p) then y:=(x)-(p);
else y:=-x-p
writeln ( 'y=',y);
end.