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 JavaScript (node.js v5.12) (judge verdict: Time Limit Exceeded)

function Main(input) {
    input = parseInt(input);
    var result = 0;
    while(input>0){
        result += checkZero(input)
        input = input -2;
    }
    console.log(result)
 
}
 
function checkZero(multi){
    var i = true;
    multi = multi.toString()
    var index=multi.toString().length-1;
    var result = 0;
    while(i){
        if(multi[index] == "0"){
            index--;
            result++;
        }
        else{
            i = false;
        }
    }
    return result;
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));