#include "trilib.h"
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N = 501;
vector<int> adj[N];
bool vis[N];
bool st[N];
int n;
bool cycle(int node) {
if (st[node]) return true;
if (vis[node]) return false;
vis[node] = true;
st[node] = true;
for (int next : adj[node]) {
if (cycle(next)) return true;
}
st[node] = false;
return false;
}
int cur = -1;
bool isGood(int node) {
for (int i = 0; i < N; i++) {
st[i] = false;
vis[i] = false;
adj[i].clear();
}
vector<int> nodes;
for (int i = 1; i <= n; i++) if (i != node) nodes.push_back(i);
int biggest = 0;
for (int i = 0; i < n - 2; i++) {
if (is_clockwise(node, nodes[i + 1], nodes[i])) biggest = nodes[i + 1];
}
for (int i = 0; i < n - 2; i++) {
if (nodes[i] == biggest) continue;
if (is_clockwise(node, nodes[i], biggest)) {
return false;
}
}
cur = biggest;
return true;
}
int getRes(int node) {
int prev = node;
int res = 1;
while (cur != node) {
int next = -1;
for (int i = 1; i <= n; i++) {
if (i == prev) continue;
if (i == cur) continue;
if (next == -1) next = i;
else {
if (is_clockwise(cur, i, next)) {
next = i;
}
}
}
prev = cur;
cur = next;
res++;
}
return res;
}
int main() {
n = get_n();
for (int i = 1; i <= n; i++) {
if (isGood(i)) {
int res = getRes(i);
give_answer(res);
break;
}
}
}
/*
6
1 1
4 3
2 2
1 4
5 1
3 2
*/
