#include <bits/stdc++.h>
#include <iostream>
#include "trilib.h"
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef tuple<int,int,int> tiii;
#define rep(i,a,b) for(int i = a; i < b; i++)
#define pb push_back
int n, guesses = 999995;
map<tiii, bool> cw;
//
// bool is_clockwise(int a, int b, int c) {
// cout << "clockwise? " << a << " " << b << " " << c << endl;
// bool ans;
// cin >> ans;
// return ans;
// }
//
// int get_n(){
// int N; cin >> N; return N;
// }
bool clockwise(int a, int b, int c){
tiii t = make_tuple(a, b, c);
if (cw.find(t) != cw.end()) return cw[t];
guesses--;
bool ans = is_clockwise(a, b, c);
cw[{a, b, c}] = cw[{b, c, a}] = cw[{c, a, b}] = ans;
cw[{a, c, b}] = cw[{c, b, a}] = cw[{b, a, c}] = !ans;
return ans;
}
int getleft(int a, set<int>& s) {
int b = *s.begin();
for (auto & c : s) {
if (c == b) continue;
if (clockwise(a, b, c)) b = c;
}
return b;
}
int getright(int a, set<int>& s) {
int b = *s.begin();
for (auto & c : s) {
if (c == b) continue;
if (!clockwise(a, b, c)) b = c;
}
return b;
}
pair<int,int> first_hull() {
int a = 1, b = 2;
// assume a top
set<int> left, right;
rep(i, 3, n + 1) {
if (clockwise(a, b, i)) left.insert(i);
else right.insert(i);
}
if (left.empty() || right.empty()) return make_pair(a, b);
int l = getleft(a, left);
int r = getright(a, right);
if (clockwise(l, r, a)) return make_pair(l, r);
else return {l, a};
}
vi sort_hull(int sortby) {
vi s = {(sortby == 1) ? 2:1};
rep(i, 1, n + 1) {
if (i == sortby || i == s[0]) continue;
int low = 0, high = s.size(), mid;
while (high - low > 1) {
mid = (high + low) / 2;
if (clockwise(sortby, i, s[mid])) high = mid;
else low = mid;
}
if (clockwise(sortby, i, s[low])) s.insert(s.begin() + low, i);
else s.insert(s.begin() + low + 1, i);
}
s.insert(s.begin(), sortby);
return s;
}
int main()
{
n = get_n();
pair<int,int> p = first_hull();
int sortby = p.first;
vi s = sort_hull(sortby);
int ans = n;
vi nxt(n+1);
rep(i,0,n-1) nxt[s[i]] = s[i + 1];
nxt[s[n - 1]] = s[0];
int cur = 1, l = 1e6;
while (guesses && l) {
l--;
if (!clockwise(cur, nxt[cur], nxt[nxt[cur]])) {
ans--;
nxt[cur] = nxt[nxt[cur]];
}
cur = nxt[cur];
}
cout << ans << endl;
}
