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. 

Examples

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.
import java.io.IOException;
import java.io.InputStream;
import java.util.InputMismatchException;

public class Solution 
{
	static InputReader in = new InputReader(System.in);
	static int mod = (int)1e9 + 7;
	static int MAXN = 100005;
	static long[] fact = new long[MAXN];
	static long[] inv = new long[MAXN];
	
    public static void main(String args[]) {
        new Thread(null, new Runnable() {
            public void run() {
                try{
                    solve();
                }
                catch(Exception e){
                    e.printStackTrace();
                }
            }
        }, "1", 1 << 26).start();
    }
    
    public static void solve(){
    	int n = in.nextInt();
    	int count = 0;
    	count = n/4 + (n % 4 == 0 ? -1 : 0);
    	if(n%2 != 0) System.out.println(0);
    	else System.out.println(count);
    }
   
    /*TEMPLATE*/
    
    //MATHS
    static int gcd(int a, int b) {
    	return (b==0)?a:gcd(b,a%b);
    }
    
    static long binPow(long x, long y) {
        long ans = 1L;
        while(y > 0) {
            if(y % 2 == 1)
                ans = mul(ans, x);
            x = mul(x, x);
            y /= 2;
        }
        return ans;
    }
    
    static long add(long x, long y) {
    	x += y;
    	return mod(x, mod);
    }
    
    static long mul(long x, long y) {
    	return mod(x * y, mod);
    }
    
    static long divide(long x, long y) {
        return mul(x, binPow(y, mod - 2));
    }

    static long mod(long x, long p) {
        x %= p;
        if (x < 0)
            x += p;
        return x;
    }
        
    public static int[] spf(int maxn) {
    	int[] spf=new int[maxn+1];
    	spf[0]=spf[1]=1;
    	for(int i=2;i<=maxn;i++) {
    		if(i%2==0) spf[i]=2;
    		else 
    			spf[i]=i;
    	}
    	for(int i=3;i*i<=maxn;i++) {
    		if(spf[i]==i){
    			for (int j=i*i; j<=maxn; j+=i) 
                    if (spf[j]==j) 
                        spf[j] = i;
    		}
    	}
    	return spf;
    }
    
    static void nCrInit() {
    	fact[0] = 1;
    	for(int i = 1; i < MAXN; i++) fact[i] = mul(fact[i - 1], 1L * i);
    	inv[MAXN - 1] = binPow(fact[MAXN - 1], mod - 2); 
    	for(int i = MAXN - 2; i >= 0; i--) inv[i] = mul(inv[i + 1], 1L * (i + 1));
     }
    
    static long nCr(int n, int r) {
    	if(r > n || n < 0 || r < 0) return 0;
    	return fact[n] * inv[r] % mod * inv[n - r] % mod;
    }
    
    //ARRAYS
    public static int[] intArray(int n) {
    	int ar[]=new int[n];
    	for(int i=0;i<n;i++)
    		ar[i]=in.nextInt();
    	return ar;
    }
    
    public static void swap(int i, int j, int ar[]) {
    	int c=ar[i];ar[i]=ar[j];ar[j]=c;
    }
    
    public static void reverse(int ar[]) {
    	int l=0, r=ar.length-1;
    	while(l<r) {
    		int temp=ar[l]; ar[l]=ar[r]; ar[r]=temp;
    		l++; r--;
    	}
    }
    
    public static int upperBound(int[] array, int value) {
    	//return next higher element. If greater than all elements then returns array.length
    	//returns 0 if smaller than all elements
    	int low = 0;
    	int high = array.length;
    	while (low < high) {
    		final int mid = (low + high) / 2;
    		if (value >= array[mid]) {
    			low = mid + 1;
    		} else {
    			high = mid;
    		}
    	}
    	return low;
    }
    
    public static int lowerBound(int[] array, int value) {
    	//Returns first occurrence.
    	//Bigger than all elements then return array.length
    	//Not found, then next greater.s
    	int low = 0;
    	int high = array.length;
    	while (low < high) {
    		final int mid = (low + high) / 2;
			if (value <= array[mid]) {
			high = mid;
			} else {
				low = mid + 1;
			}
    	}
    	return low;
	}
    
    public static void pn(Object o) {
      System.out.println(o);
    }
    
    static class InputReader {
 
        private InputStream stream;
        private byte[] buf = new byte[8192];
        private int curChar;
        private int snumChars;
        private SpaceCharFilter filter;
 
        public InputReader(InputStream stream) {
            this.stream = stream;
        }
 
        public int snext() {
            if (snumChars == -1)
                throw new InputMismatchException();
            if (curChar >= snumChars) {
                curChar = 0;
                try {
                    snumChars = stream.read(buf);
                } catch (IOException e) {
                    throw new InputMismatchException();
                }
                if (snumChars <= 0)
                    return -1;
            }
            return buf[curChar++];
        }
 
        public int nextInt() {
            int c = snext();
            while (isSpaceChar(c))
                c = snext();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = snext();
            }
 
            int res = 0;
 
            do {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = snext();
            } while (!isSpaceChar(c));
 
            return res * sgn;
        }
 
        public long nextLong() {
            int c = snext();
            while (isSpaceChar(c))
                c = snext();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = snext();
            }
 
            long res = 0;
 
            do {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = snext();
            } while (!isSpaceChar(c));
 
            return res * sgn;
        }
 
        public String readString() {
            int c = snext();
            while (isSpaceChar(c))
                c = snext();
            StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = snext();
            } while (!isSpaceChar(c));
            return res.toString();
        }
 
        public boolean isSpaceChar(int c) {
            if (filter != null)
                return filter.isSpaceChar(c);
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }
 
        public interface SpaceCharFilter {
            public boolean isSpaceChar(int ch);
        }
    }
}