5,6 |
| :---: | :---: | :---: |
|  | Classical combinatorics (miscellaneous). |  |
|  | Examples and counterexamples. Constructions |  |
|  | Estimation + example |  |

Each of thirty sixth-graders has one pen, one pencil, and one ruler. After their participation in the Olympiad, it turned out that 26 students lost their pen, 23 - their ruler, and 21 - their pencil. Find the smallest possible number of sixth-graders who lost all three items.