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 C (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<stdio.h>

unsigned int fun(unsigned int n)
{
    if (n<2)  return 1;
    return n * fun(n-2);
}

unsigned int  trail(unsigned int n)
{
    int count = 0;
    while(n!=0)
    {
        if (n & 1 == 1)    break;
        n = n>>1;
        count++;
    }
    return count;
}

int main()
{
    unsigned int num, fact, t_zero;
    printf("Enter a number: ");
    scanf("%d", &num);
    fact = fun(num);
     t_zero = trail(fact);
     printf("%d", t_zero);
}