I'm having trouble converting data received over UART to a number (I know seems simple...) msg is [u8; 64]

```
if msg.starts_with("MAP".as_bytes()){
        let count = msg.strip_prefix("MAP".as_bytes()).unwrap();
        let count = str::from_utf8(count).unwrap(); // this seems to be "2"
        let count = count.trim().parse::<usize>().unwrap();
...
```
I am getting an invalid digit error