Source: https://www.iuventa.sk/files/documents/2_olympiady/onj/26.%20ro%C4%8Dn%C3%ADk/%C3%BAlohy%20a%20rie%C5%A1enia/celo%C5%A1t%C3%A1tne%20kolo/n26ck1bulri16.pdf