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: Runtime Error)


import java.util.Scanner;

public class Main {
    public static void main(String[] args) {

        Scanner scan = new Scanner(System.in);

        int n = scan.nextInt();
        int res = factorial(n);
        String str = Integer.toString(res);
        StringBuilder rev = new StringBuilder(str);
        String s = rev.reverse().toString();
        String[] st = s.split("");
        int count = 0;
        for (int i=0; i<st.length; i++){
            if (st[i].contains("0")) {
                count += 1;
            } else {
                break;
            }
        }
        System.out.println(count);
    }

    public static int factorial(int a){
        return (a<2)?1:a*factorial(a-2);
    }
}