var x, y:real;
begin
readln(x);
if (x<=-4) or (x>=4) then
y:=0
else if (x>-4) and (x<0) then
y:= -sqrt(4-(x+2)*(x+2))
else if (x>=0) and (x<4) then
y:=sqrt(4-(x-2)*(x-2));
write(y);
end.
