Cambio de dificultad reto 4

Author: Achalogy

README.md

@@ -13,7 +13,7 @@ Repositorio donde estoy subiendo y explicando los retos del Advent JS 2023.
 | <img src="https://adventjs.dev/challenges-2023/1.png" width="50" style="object-fit: contain;" /> | 01  | [🎁 ¡Primer regalo repetido!](https://adventjs.dev/es/challenges/2023/1)        | 🟢             | [Ver](https://github.com/Achalogy/advent-js-2023/blob/main/retos/reto-1/README.md) | [SPOILER](https://github.com/Achalogy/advent-js-2023/blob/main/retos/reto-1/main.ts) | ~~~~~ |
 | <img src="https://adventjs.dev/challenges-2023/2.png" width="50" style="object-fit: contain;" /> | 02  | [🏭 Ponemos en marcha la fábrica](https://adventjs.dev/es/challenges/2023/2)    | 🟢             | [Ver](https://github.com/Achalogy/advent-js-2023/blob/main/retos/reto-2/README.md) | [SPOILER](https://github.com/Achalogy/advent-js-2023/blob/main/retos/reto-2/main.ts) | ~~~~~ |
 | <img src="https://adventjs.dev/challenges-2023/3.png" width="50" style="object-fit: contain;" /> | 03  | [😏 El elfo travieso](https://adventjs.dev/es/challenges/2023/3)                | 🟢             | [Ver](https://github.com/Achalogy/advent-js-2023/blob/main/retos/reto-3/README.md) | [SPOILER](https://github.com/Achalogy/advent-js-2023/blob/main/retos/reto-3/main.ts) | ~~~~~ |
-| <img src="https://adventjs.dev/challenges-2023/4.png" width="50" style="object-fit: contain;" /> | 04  | [😵‍💫 Dale la vuelta a los paréntesis](https://adventjs.dev/es/challenges/2023/4) | 🟢+[^2]        | [Ver](https://github.com/Achalogy/advent-js-2023/blob/main/retos/reto-4/README.md) | [SPOILER](https://github.com/Achalogy/advent-js-2023/blob/main/retos/reto-4/main.ts) | ~~~~~ |
+| <img src="https://adventjs.dev/challenges-2023/4.png" width="50" style="object-fit: contain;" /> | 04  | [😵‍💫 Dale la vuelta a los paréntesis](https://adventjs.dev/es/challenges/2023/4) | 🟠             | [Ver](https://github.com/Achalogy/advent-js-2023/blob/main/retos/reto-4/README.md) | [SPOILER](https://github.com/Achalogy/advent-js-2023/blob/main/retos/reto-4/main.ts) | ~~~~~ |
 | <img src="https://adventjs.dev/challenges-2023/5.png" width="50" style="object-fit: contain;" /> | 05  | [🛷 El CyberTruck de Santa](https://adventjs.dev/es/challenges/2023/5)          | 🟠             | [Ver](https://github.com/Achalogy/advent-js-2023/blob/main/retos/reto-5/README.md) | [SPOILER](https://github.com/Achalogy/advent-js-2023/blob/main/retos/reto-5/main.ts) | ~~~~~ |
 | <img src="https://adventjs.dev/challenges-2023/6.png" width="50" style="object-fit: contain;" /> | 06  | [🦌 Los renos a prueba](https://adventjs.dev/es/challenges/2023/6)              | 🟢             | [Ver](https://github.com/Achalogy/advent-js-2023/blob/main/retos/reto-6/README.md) | [SPOILER](https://github.com/Achalogy/advent-js-2023/blob/main/retos/reto-6/main.ts) | ~~~~~ |
 |                                                                                                  | 07  | ~~~~~                                                                           |                | ~~~~~                                                                              | ~~~~~                                                                                | ~~~~~ |