/*DavitMarg*/
#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <string>
#include <cstring>
#include <map>
#include <set>
#include <queue>
#include <iomanip>
#include <stack>
#include <cassert>
#include <iterator>
#include <bitset>
#include <fstream>
#ifndef death
#include<trilib.h>
#endif // death
#define mod 1000000007ll
#define LL long long
#define LD long double
#define MP make_pair
#define PB push_back
#define all(v) v.begin(),v.end()
using namespace std;
#ifdef death
int get_n()
{
cout << "N::" << endl;
int x;
cin >> x;
return x;
}
bool is_clockwise(int a, int b, int c)
{
cout << ":::" << a << " " << b << " " << c << endl;
int x;
cin >> x;
return x;
}
void give_answer(int x)
{
cout << x << endl;
}
#endif // death
map<pair<int, pair<int, int>>, bool> used, pre;
bool cw(int a, int b, int c)
{
if (a == b || b == c || c == a)
return 1;
if (used[MP(a, MP(b, c))])
return pre[MP(a, MP(b, c))];
used[MP(a, MP(b, c))] = 1;
return pre[MP(a, MP(b, c))] = is_clockwise(a, b, c);
}
bool ccw(int a, int b, int c)
{
if (a == b || b == c || c == a)
return 1;
return !cw(a, b, c);
}
int convex(vector<int> p)
{
vector<int> up, down;
vector<bool> uUp(p.size() + 5), uDown(p.size() + 5);
int st, en;
st = p[0];
en = p.back();
reverse(all(p));
p.pop_back();
reverse(all(p));
p.pop_back();
vector<int> add = p;
p.clear();
p.PB(st);
for (int i = 0; i < add.size(); i++)
for (int j = 0; j < add.size(); j++)
p.PB(add[j]);
p.PB(en);
up.PB(p[0]);
down.PB(p[0]);
for (int i = 1; i < p.size(); i++)
{
if (i == p.size() - 1 || (!uUp[p[i]] && cw(p[0], p[i], p[p.size() - 1])))
{
while (up.size() > 1 && (!cw(up[up.size() - 2], up[up.size() - 1], p[i]) || up.back() == p[i]))
{
uUp[up.back()] = 0;
up.pop_back();
}
up.PB(p[i]);
uUp[up.back()] = 1;
}
if (i == p.size() - 1 || (!uDown[p[i]] && ccw(p[0], p[i], p[p.size() - 1])))
{
while (down.size() > 1 && (!ccw(down[down.size() - 2], down[down.size() - 1], p[i]) || down.back() == p[i]))
{
uDown[down.back()] = 0;
down.pop_back();
}
down.PB(p[i]);
uDown[down.back()] = 1;
}
}
down.pop_back();
reverse(all(down));
down.pop_back();
reverse(all(down));
while (!down.empty())
{
up.PB(down.back());
down.pop_back();
}
for (int i = 0; i < up.size(); i++)
if (!cw(up[i], up[(i + 1) % up.size()], up[(i + 2) % up.size()]))
return 0;
return up.size();
}
int ans, n;
vector<int> p;
int main()
{
n = get_n();
for (int i = 1; i <= n; i++)
p.PB(i);
for (int i = 0; i < n; i++)
for (int j = 0; j < n; j++)
{
if (i == j)
continue;
swap(p[0], p[i]);
swap(p.back(), p[j]);
ans = max(ans, convex(p));
swap(p[0], p[i]);
swap(p.back(), p[j]);
}
give_answer(ans);
return 0;
}
/*
4
1
0
0
0
1
1
*/
