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: Accepted)

int main()
{
	long n;
	long cnt = 0;
	

	scanf("%ld", &n);

	//printf("%ld\n",n);
	if (n % 2 == 1) {
		cnt = 0;
	}
	else {
		if (n > 0) {
			cnt += n / 10;
			n /= 10;
		}

		while (n > 0) {
			
			cnt += n / 5;
			n /= 5;
		}
	}
	

	printf("%ld", cnt);
	
}