Problem link: https://atcoder.jp/contests/abc259/tasks/abc259_b

Submission link(WA): https://atcoder.jp/contests/abc259/submissions/33131531

Submission link(AC): https://atcoder.jp/contests/abc259/submissions/33131108

The only change I have done is how I am calculating the angle. I am getting wrong answer when I use atan, however I am getting AC with atan2.

ld ang;
  if(a == 0){
    if(b > 0) ang = PI/2;
    else ang = -PI/2;
  } else ang = atan((ld)b/a);