Compute Factorial Trailing Zeros

Given a non-negative integer n, calculate the number of trailing zeros in n!. The number of trailing zeros in a factorial is determined by the number of times 10 is a factor in the product. Since 10 is made by multiplying 2 and 5, and there are always more factors of 2, you need to count the factors of 5. Input a single integer, and output the number of trailing zeros in its factorial. Example Input: 25 Example Output: 6