PROGRAMMING:Credit difference (*)

This semester, Xiao Zhang completed $$Z $$credits and Xiao Wang completed $$W $$credits. How many credits is the difference between them?
####Input format
>$$Z $$and $$W$$
####Output format
>Credit difference
####Input sample 1
```in
17 23
```
####Output sample 1
```out
six
```
####Input sample 2
```in
25 21
```
####Output sample 2
```out
four
```







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