ACSL Practice 2009

The factorial of a positive integer ~n~, written as ~n!~, is the product of the first ~n~ positive integers. That is,

$$\displaystyle n! = 1 \times 2 \times \dots \times n$$

Given a positive integer ~n~, find the number of zeros in the decimal representation of ~n!~. Of course, leading zeros should not be counted. (Note that decimal representation means base ten representation.)

Example 1. There are ~7~ zeros in the decimal representation of ~20!~.

$$\displaystyle 20! = 1 \times 2 \times \dots \times 20 = 2432902008176640000$$

Example 2. There are ~2~ zeros in the decimal representation of ~7!~.

$$\displaystyle 7! = 1 \times 2 \times 3 \times 4 \times 5 \times 6 \times 7 = 5040$$

Example 3. There is no zero in the decimal representation of ~4!~.

$$\displaystyle 4! = 1 \times 2 \times 3 \times 4 = 24$$

Input Specification

The input contains a single positive integer ~n \le 100~.

Output Specification

The number of zeros in the decimal representation of ~n!~.

Sample Input 1

20

Sample Output 1

7

Sample Input 2

7

Sample Output 2

2

Sample Input 3

4

Sample Output 3

0