What is the answer for test:
4 10
0 10
10 0
1 1
5 -5

YES
+--+

But after three steps P = (0,10) - (10,0) - (1,1) = (-11,9);
Distance to Z = (0,0) equal to sqrt(11*11+9*9) = sqrt(202) = 14.2126 > sqrt(2)*10 = 14.1421

Hmm, well, you might be onto something!
The thing is, my program doesn't have "WRONG ANSWER" in it at all, and now that i look at it again i don't really remember why :)
You can try to email one of the admins about this.

Edit @below: ohhh right. By now i already forgot about this detail. Thanks!

Edited by author 26.09.2016 16:04

"...and she wants him to move off her not farther than by the square root of 2 multiplied by L (sqrt(2)L)
IN THE END OF HIS WALK."

Your case describes the distance after 3 steps, not 4. Nikifor is allowed to move farther in the middle of the  travel.

Edited by author 26.09.2016 14:36

Edited by author 26.09.2016 14:36

My AC give:
YES
+-++