# Can you solve this puzzle?

Level pending

Solve this logic number sequence puzzle by guessing the correct digit:

\begin{align*} f(8080) &= 6 \\ f(1357) &= 0 \\ f(2022) &= 1 \\ f(1999) &= 3 \\ f(6666) &= \text{ ?} \end{align*}

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