**The first real hint will be published on 14th March**. Meanwhile, here are the clarification regarding the grading of Problem 3. **Rule 1: **if all frequencies are wrong, the solution is considered as incorrect, i.e. the factor 0.9 will be applied once a correct solution is submitted at a later time.**Rule 2: **if at least one frequency is correct (regardless if the number of modes is correct), the solution is considered as almost correct, i.e. the factor 0.95 will be applied once a correct solution is submitted at a later time.**Rule 3:** if only one correct frequency is missing AND there is no mistakes or only one mistake with the number of modes for the correct frequencies, the factor 0.975 will be applied once a correct solution is submitted at a later time.**Rule 4:** if all the frequencies have been found correctly, but there is one (more than one) mistake with the number of modes, the solution is accepted as a correct one, but the score is lowered to 0.975 (0.95).**Rule 5:** if some mistakes are corrected by the contestant before the publication of the intermediate results, the remaining penalty is calculated as the average of the initial and final penalties. For instance: initially wrong (0.9), corrected to almost correct (0.95) will yield a penalty of 0.925 once a correct solution is submitted at a later time. Almost correct solution is corrected to a correct one, with one mistake in the number of modes will yield a penalty of 0.9625 while the solution is accepted as is.

*Please submit the solution of this problem via e-mail to physcs.cup@gmail.com.** *

* For full regulations, see the “Participate” tab.*