var  a,b,x,R:real;
begin
writeln ('Ââåäèòå ÷èñëî a,b,x');
readln(a,b,x);
R:=(4.8+1/(tan(x*x)*tan(x*x)))/(2*(a-b)*ln(power(a,3)+x));
writeln (R:0:3);
end.