// DK, poreted Mateusz Radecki solution
//import java.util.*;
import java.util.Arrays;
import java.util.*;
class vector {
int[] data = new int[40*1000 + 15];
public int size = 0;
public int at(int i) {
return data[i];
}
public void set(int i, int x) {
data[i] = x;
}
public int back() {
return data[size-1];
}
public void push_back(int x) {
data[size] = x;
++size;
}
public void pop_back() {
--size;
}
public void push_front(int x) {
for(int i = size; i > 0; --i) {
data[i] = data[i-1];
}
data[0] = x;
++size;
}
void swap(int i, int j) {
int tmp = data[i];
data[i] = data[j];
data[j] = tmp;
}
public void reverse(int p, int q) {
--q;
while(p < q) {
swap(p, q);
++p;
--q;
}
}
boolean is_less(int a, int b) {
return trilib.is_clockwise(1, a, b);
}
Integer[] take_copy() {
Integer[] ret = new Integer[size];
for(int i = 0; i < size; ++i) {
ret[i] = new Integer(data[i]);
}
return ret;
}
public void mySort() {
Integer[] sorted = take_copy();
Arrays.sort(sorted, new Comparator<Integer>() {
public int compare(Integer o1, Integer o2) {
return 1 - 2 * (trilib.is_clockwise(1, (int)o1, (int)o2) ? 1 : 0);
}
});
for(int i = 0; i < size; ++i) {
data[i] = sorted[i];
}
}
public void swap_with(vector b) {
int r = b.size;
int[] d = b.data;
b.data = data;
b.size = size;
data = d;
size = r;
}
}
public class tri {
static int n;
static vector[] divide = new vector[2];
static vector[] hull = new vector[2];
public static void main(String[] args) {
for(int i = 0; i < 2; ++i) {
divide[i] = new vector();
hull[i] = new vector();
}
n = trilib.get_n();
for(int i=3; i<=n; i++) {
divide[trilib.is_clockwise(1, 2, i) ? 1 : 0].push_back(i);
}
for(int h = 0; h<2; ++h) {
divide[h].push_back(2);
divide[h].mySort();
for (int i=0; i < divide[h].size; i++) {
int r = hull[h].size;
while (r>1 && !trilib.is_clockwise(hull[h].at(r-2), hull[h].at(r-1), divide[h].at(i))) {
r--;
hull[h].pop_back();
}
hull[h].push_back(divide[h].at(i));
}
if(h > 0) {
hull[h].reverse(0, hull[h].size);
}
hull[h].push_front(1); // wloz?
}
for(int h=0; h<2; h++) {
hull[0].pop_back();
while(true) {
int out = 1;
int r = hull[0].size;
if (r>1 && !trilib.is_clockwise(hull[0].at(r-2), hull[0].at(r-1), hull[1].back())) {
hull[0].pop_back();
out=0;
}
int d=hull[1].size;
if (d>1 && !trilib.is_clockwise(hull[0].back(), hull[1].at(d-1), hull[1].at(d-2))) {
hull[1].pop_back();
out=0;
}
if (out > 0) {
break;
}
}
for (int i=0; i<2; i++) {
hull[i].reverse(0, hull[i].size);
}
hull[0].swap_with(hull[1]);
}
trilib.give_answer(hull[0].size + hull[1].size);
}
};
