Count Number of F's

Out of how many F's does the following sentence consist?
FINISHED FILES ARE THE RESULTS OF YEARS OF SCIENTIFIC STUDY COMBINED WITH THE
EXPERIENCE OF YEARS.

Your Count May Be WRONG!

In Between Wrong Count Of F's

Take a look at sentence once again!

Did you count only 3? Really? Here is that sentence written once again.

FINISHED FILES ARE THE RESULTS OF YEARS OF SCIENTIFIC STUDY COMBINED WITH THE
EXPERIENCE OF YEARS.

So didn't you count F of word 'OF'? Now how many F's you are finding? 

And that's right! There are 6 F's in the sentence.