# Trailing Zeros

Learn to write the code for counting the number of trailing zeros at the end of a factorial.

## We'll cover the following

## Challenge

Write a function called `countTrailingZeros (int X)`

that determines the number of trailing zeros at the end of X! (X factorial), where X is an arbitrary input from the user.

**Note:** In case of a negative number X, your program should return -1.

## Example 1

Input: 12

12! = 479001600

Number of zeros at the end of 12! = 2

## Example 2

Input: 5

5! = 120

Number of zeros at the end of 5! = 1

## Example 3

Input: -20

Number of zeros at the end of -20! = -1

## Coding exercise

Try to solve this challenge on your own. If you can’t solve it, you can look at the solution and explanation below.

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