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 Pascal (FPC 2.6.2) (judge verdict: Wrong Answer)

uses crt;
var count,b,n,i: longint;
begin
clrscr;
read(n);
b:=n;
repeat
for i:=1 to b do
if i mod 5 =0 then  inc(count);
b:=b div 5;
until b<5;
if n mod 2 = 0 then write(count div 2) else write('0');
readln;
readln;
end.