What does WA mean in a challenge problem?

Problem: https://www.codechef.com/DEC18B/problems/DLDAG
I am getting WA in this. This is the first time I’m attempting a challenge problem. I had the impression that challenge problems have only approximate solutions so whatever value of S I print I’d get a zero(though this is not what I did actually). What does WA mean here? Is it that a smaller value of S exist? Isn’t that impossible to find in the given time limit? Please explain the concept of challenge problems to me. Thanks!

In the scoring section . it is clearly mentioned
However, if your program gets a non-AC verdict on any test file, your submission's verdict will be non-AC.
you have to print the the value of min number of steps and regarding division , it is a float/floar division giving a float result . that’s why people are getting score in decimals .