An amateur magician wanted to prepare a magic trick. He had to always be able to guess the minimum number of times he needed to pick up at least one of each $3$ coloured balls. A participant was holding a bag with $8$ blue balls, $10$ red balls and $13$ green balls. Can you help out the amatuer magician and determine the minimum number of balls the amateur needed to pick? 
Overseas Competition->Knowledge Point->Combinatorics->Pigeonhole Principle