An astronaut named Mark, arrived to mars to collect some rock samples for earth. He collected 3 unique types of stones. Igneous rock, sedimentary rock and metamorphic. Unfortunately, he was running out of oxygen and didnt have the time to label the sacks he put each rock type in. The result was that he mislabeled all the sacks. How many rocks did he have to take out of how many sacks in order to find out what rock belongs to which sack?