Problem:
Score : 500 points

Problem Statement

For an integer n not less than 0, let us define f(n) as follows:

f(n) = 1 (if n < 2)

f(n) = n f(n-2) (if n \geq 2)

Given is an integer N. Find the number of trailing zeros in the decimal notation of f(N).

Constraints

0 \leq N \leq 10^{18}

Input

Input is given from Standard Input in the following format:

N

Output

Print the number of trailing zeros in the decimal notation of f(N).

Sample Input 1

12

Sample Output 1

1

f(12) = 12 × 10 × 8 × 6 × 4 × 2 = 46080, which has one trailing zero.

Sample Input 2

5

Sample Output 2

0

f(5) = 5 × 3 × 1 = 15, which has no trailing zeros.

Sample Input 3

1000000000000000000

Sample Output 3

124999999999999995

Solution in Java (OpenJDK 11.0.6) (judge verdict: Wrong Answer)

import java.util.*;
 
class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    long N = Long.parseLong(sc.next());
    long R = 0;
    if(N%2==0){
      long subN = N/2;
      boolean escape = false;
      for(int i = 1;!escape;i++){
        if(subN/5!=0){
          R+=subN/5;
          subN=subN/5;
        }else{
          escape = true;
        }
      }
      System.out.println(R);
    }
  }
}