#include <bits/stdc++.h>
#include "trilib.h"
using namespace std;
//#pragma GCC optimize ("O3")
//#pragma GCC target ("sse4")
#ifndef LOCAL
#define cerr if(false) cerr
#endif
#define endl "\n"
#define all(x) (x).begin(), (x).end()
#define forn(i, n) for(int i = 0; i < n; i ++)
#define revn(i, n) for(int i = n - 1; i >= 0; i --)
typedef long long ll;
template<class T, template<class T2, class A=allocator<T2> > class cont> inline ostream &operator <<(ostream &out, const cont<T> &x) { for(const auto &it : x) { out << it << " ";} return out;}
template<class T, template<class T2, class A=allocator<T2> > class cont> inline istream &operator >>(istream &in, cont<T> &x) { for(auto &it : x) { in >> it;} return in;}
template<class T, class T2> inline ostream &operator <<(ostream &out, const pair<T, T2> &x) { out << x.first << " " << x.second; return out;}
template<class T, class T2> inline istream &operator >>(istream &in, pair<T, T2> &x) { in >> x.first >> x.second; return in;}
template<class T, class T2> inline bool chkmax(T &x, const T2 &y) { return x < y ? x = y, 1 : 0; }
template<class T, class T2> inline bool chkmin(T &x, const T2 &y) { return x > y ? x = y, 1 : 0; }
const ll mod = 1e9 + 7;
signed main() {
// ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
int n;
int special = 1;
n = get_n();
vector<int> vert;
forn(i, n) {
if(i + 1 != special) {
vert.push_back(i + 1);
}
}
sort(all(vert), [&special](const int a, const int b) {
return is_clockwise(special, a, b) == true;
});
reverse(all(vert));
vert.push_back(special);
reverse(all(vert));
vector<int> st;
for(auto it : vert) {
while(!(st.size() < 2) && !is_clockwise(st[st.size() - 2], st[st.size() - 1], it)) {
st.pop_back();
}
st.push_back(it);
}
int ret = st.size();
auto cpy = st;
for(auto it : cpy) {
while(!(st.size() < 2) && !is_clockwise(st[st.size() - 2], st[st.size() - 1], it)) {
st.pop_back();
ret --;
}
st.push_back(it);
}
give_answer(ret);
return 0;
}
