Cyrus walked through the huge door, which leaded to a hollow tunnel. It was very dark inside, so Cyrus lit up his torch. He walked through the tunnel, but he couldn't see any exit, except for where he came from. Cyrus knew that he mustn't give up, so he searched more carefully. Suddenly, he saw two letters on the wall: A and U. Under the two letters was also a mini keyboard which only has numbers and decimal point. There were 5 blanks under the keyboard. Cyrus tried typing random numbers, but a buzzer rang when he entered 5 numbers. That must be a wrong answer, Cyrus thought. Can you solve the problem for Cyrus?
I will publish the correct answer if no one has the right answer