var
 s1,s2:real;
begin
     writeln('#########################');
     write('R (kolca) = ');
     readln(s2);
     write('R (otverstia) = ');
     readln(s1);
     if (s1>=s2) then writeln('Error : R(otverstia) >= R(kolca)')
     else writeln('S (kolca) = ',pi*(s2*s2-s1*s1):3:3);
end.