Factorial Zeros

Factorial Zeros

Simple+

Write a function that finds the number of zeros at the end of the decimal expansion of factorial n!. Because factorials grow very fast, it is not a good strategy to calculate n! and count the zeros.

example

Input: Integer (int).

Output: Integer (int).

Examples: 

assert fact_zeros(2) == 0
assert fact_zeros(5) == 1
assert fact_zeros(20) == 4

This mission was taken from WOLFRAM CHALLENGES

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freeman_lex
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