## Pair of Socks

Joseph is in the middle of packing for a vacation. He's having a bit of trouble finding all of his socks, though.

Write a function that returns the number of sock pairs he has. A sock pair consists of two of the same letter, such as `"AA"`. The socks are represented as an unordered sequence.

### Examples

```text
SockPairs("AA") ➞ 1

SockPairs("ABABC") ➞ 2

SockPairs("CABBACCC") ➞ 4
```

---

### Notes

- If given an empty string (no socks in the drawer), return 0.
- There can be multiple pairs of the same type of sock, such as two pairs of CC for the last example.