Codeforces Round #337 (Div. 2) A水

A. Pasha and Stick

time limit per test

1 second

memory limit per test

256 megabytes

input

standard input

output

standard output

Pasha has a wooden stick of some positive integer length n. 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 be n.

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 integer x, such that the number of parts of length x in the first way differ from the number of parts of length x in the second way.

Input

The first line of the input contains a positive integer n (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 test(s)

Input

6

Output

1

Input

20

Output

4

Note

There is only one way to divide the stick in the first sample {1, 1, 2, 2}.

Four ways to divide the stick in the second sample are {1, 1, 9, 9}, {2, 2, 8, 8}, {3, 3, 7, 7} and {4, 4, 6, 6}. Note that {5, 5, 5, 5} doesn't work.

应该是今年最后一次做cf了 时间很良心 但是自己确实水  只做出a woc 以后打cf 不能再求援于任何人 必须靠自己

len 为周长 求有多少种组成长方形但不是正方形的组合

！！！

#include<bits/stdc++.h>
using namespace std;
#define LL __int64
int main()
{
    LL len;
    scanf("%I64d",&len);
    if(len<4||len%2==1)
    printf("0\n");
    else
    {
    len=len/2;
    if(len%2==0)
    printf("%I64d\n",len/2-1);
    else
        printf("%I64d\n",len/2);
    }
    return 0;
}