[US] [Day 7-Part 2] I want to know the size of the directoy I must delete

## Story

**As** Santa Claus 
**I want to** know the size of the smallest directory to delete
**So** I can delete it

## Test data

```
$ cd /
$ ls
dir a
14848514 b.txt
8504156 c.dat
dir d
$ cd a
$ ls
dir e
29116 f
2557 g
62596 h.lst
$ cd e
$ ls
584 i
$ cd ..
$ cd ..
$ cd d
$ ls
4060174 j
8033020 d.log
5626152 d.ext
7214296 k
```

Will return a size of `24933642`