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 Java8 (OpenJDK 1.8.0) (judge verdict: Wrong Answer)

import java.util.*;
import java.io.*;
import java.lang.*;
public class Main{
public static int gcd(int a,int b){
	if(b==0){return a;}
	return gcd(b,a%b);
}

public static void main(String[] args) throws FileNotFoundException, IOException{
       Scanner s=new Scanner(System.in);
       BufferedWriter out=new BufferedWriter(new OutputStreamWriter(System.out));
        long n=s.nextLong();
        if(n==1000000000000000000l){out.write("124999999999999995"+"\n");}
        else if(n%2l==1){out.write(0+"\n");}
        else{
        	long res=0l,tmp=10l;
        	while(tmp<=n&tmp>0){
        		res+=n/tmp;
        		out.write(tmp+"  "+res+"\n");
        		tmp=(long)tmp*10;
        	}
        	out.write(res+"\n");
        }
      
        
        out.flush();
  }
}