var i:integer;
s,v:real;
Begin
read(i,v);
case i of
1: s:=pi*v*v;
2: s:=pi*v*v/4;
3: s:=v*v/pi/4;
end;
writeln(s);
End.
var i:integer;
s,v:real;
Begin
read(i,v);
case i of
1: s:=pi*v*v;
2: s:=pi*v*v/4;
3: s:=v*v/pi/4;
end;
writeln(s);
End.