#include <bits/stdc++.h> // Tomasz Nowak
#include "trilib.h"
using namespace std; // XIII LO Szczecin
using LL = long long; // Poland
#define FOR(i, l, r) for(int i = (l); i <= (r); ++i)
#define REP(i, n) FOR(i, 0, (n) - 1)
template<class T> int size(T &&x) {
return int(x.size());
}
template<class A, class B> ostream& operator<<(ostream &out, const pair<A, B> &p) {
return out << '(' << p.first << ", " << p.second << ')';
}
template<class T> auto operator<<(ostream &out, T &&x) -> decltype(x.begin(), out) {
out << '{';
for(auto it = x.begin(); it != x.end(); ++it)
out << *it << (it == prev(x.end()) ? "" : ", ");
return out << '}';
}
void dump() {}
template<class T, class... Args> void dump(T &&x, Args... args) {
cerr << x << "; ";
dump(args...);
}
#ifdef DEBUG
struct Nl{~Nl(){cerr << '\n';}};
# define debug(x...) cerr << (strcmp(#x, "") ? #x ": " : ""), dump(x), Nl(), cerr << ""
#else
# define debug(...) 0 && cerr
#endif
mt19937_64 rng(0);
int rd(int l, int r) {
return uniform_int_distribution<int>(l, r)(rng);
}
// end of templates
bool dir_right(int a, int b, int c) {
return is_clockwise(a + 1, b + 1, c + 1);
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
int n = get_n();
debug(n);
array<vector<int>, 2> halfplane;
FOR(i, 2, n - 1)
halfplane[dir_right(0, 1, i)].emplace_back(i);
debug(halfplane);
array<vector<int>, 2> halfhull;
REP(iter, 2) {
halfplane[iter].emplace_back(1);
sort(halfplane[iter].begin(), halfplane[iter].end(), [&](int a, int b) {
if(a == b)
return false;
return dir_right(0, a, b) != iter;
});
halfplane[iter].emplace(halfplane[iter].begin(), 0);
debug(halfplane[iter]);
auto &hp = halfplane[iter], &hh = halfhull[iter];
for(int p : hp) {
while(size(hh) >= 2 and dir_right(hh.end()[-2], hh.back(), p) == iter)
hh.pop_back();
hh.emplace_back(p);
}
debug(iter, hh);
if(iter)
hh.erase(prev(hh.end()));
else
hh.erase(hh.begin());
debug(iter, hh);
}
REP(iter, 2) {
for(auto &hh : halfhull)
reverse(hh.begin(), hh.end());
debug(halfhull);
while(true) {
bool did = false;
if(size(halfhull[0]) >= 2 and size(halfhull[1]) >= 1
and dir_right(halfhull[0].end()[-2], halfhull[0].back(), halfhull[1].back()) != iter) {
halfhull[0].pop_back();
did = true;
}
if(size(halfhull[0]) >= 1 and size(halfhull[1]) >= 2
and dir_right(halfhull[0].back(), halfhull[1].back(), halfhull[1].end()[-2]) != iter) {
did = true;
halfhull[1].pop_back();
}
if(not did)
break;
}
}
debug(halfhull);
give_answer(size(halfhull[0]) + size(halfhull[1]));
}
