I submitted some algo which on my computer gives correct result for sample input given in problem statement and I got WA in test #1. Then I tried this code:

public class Problem_1285 {
    public static void main(String[] args) {
        System.out.println("1.00");
    }
}

...and got the same WA #1. What's going on???

Seems like test #1 is not the sample test

It is often the case.