Let **R** be the language described by the following regular expression:

```
(a|b)*(c|d)e?f+
```

How many of the following strings are NOT members of **R**?

```
abc, aabbd, df, abbcdf, abdef, bbacf,
abbbbbbdef, aabbcef, abbceef, abababcf,
abcdf, f, ef, def, be, abe, acef
```

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