Pasha and Stick（纯数学问题）

                                                             Pasha and Stick

Time Limit:1000MS    Memory Limit:262144KB    64bit IO Format:%I64d & %I64u

SubmitStatus

Description

Pasha has a wooden stick of some positive integer lengthn. He wants to perform exactly three cuts to get four parts of the stick. Each part must have some positive integer length and the sum of these lengths will obviously ben.

Pasha likes rectangles but hates squares, so he wonders, how many ways are there to split a stick into four parts so that it's possible to form a rectangle using these parts, but is impossible to form a square.

Your task is to help Pasha and count the number of such ways. Two ways to cut the stick are considered distinct if there exists some integerx, such that the number of parts of lengthx in the first way differ from the number of parts of lengthx in the second way.

Input

The first line of the input contains a positive integern (1 ≤ n ≤ 2·10⁹) — the length of Pasha's stick.

Output

The output should contain a single integer — the number of ways to split Pasha's stick into four parts of positive integer length so that it's possible to make a rectangle by connecting the ends of these parts, but is impossible to form a square.

Sample Input

Input

6

Output

1

Input

20

Output

4
给出木棍长n,砍三下，问有多少种组成长方形的方法
#include<stdio.h>
#include<iostream>
#include<algorithm>
using namespace std;
int main(){
    __int64 n,l1,l2,i;
    while(~scanf("%I64d",&n))
		{
        int k = 0;
        if(n%2!=0){
        printf("0\n");
            continue;
        }
        for(i=1;i<=n/4;i++)
			{
            l1 = n/2-i;
             l2 = n/2-i-l1;
            if(l2==0&&l1!=i&&l1>0){
                k++;
            }
        }
       printf("%d\n",k);
    }
    return 0;
}