#define _CRT_SECURE_NO_WARNINGS
#include "trilib.h"
#include <bits/stdc++.h>
//#include <ext/pb_ds/tree_policy.hpp>
//#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
//using namespace __gnu_pbds;
#define FOR(i,start,end) for(int i=start;i<(int)(end);i++)
#define FORE(i,start,end) for(int i=start;i<=(int)end;i++)
#define RFOR(i,start,end) for(int i = start; i>end; i--)
#define RFORE(i,start,end) for(int i = start; i>=end; i--)
#define all(a) a.begin(), a.end()
#define mt make_tuple
#define mp make_pair
#define v vector
#define sf scanf
#define pf printf
#define dvar(x) cout << #x << " := " << x << "\n"
#define darr(x,n) FOR(i,0,n) cout << #x << "[" << i << "]" << " := " << x[i] << "\n"
typedef long long ll;
typedef long double ld;
typedef pair<int, int > pii;
typedef pair<ll, ll> pll;
//template <class T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template<class T> void minn(T &a, T b) { a = min(a, b); }
template<class T> void maxx(T &a, T b) { a = max(a, b); }
void io() {
#ifdef LOCAL_PROJECT
freopen("input.in", "r", stdin); freopen("output.out", "w", stdout);
#else
/* online submission */
#endif
ios_base::sync_with_stdio(false); cin.tie(NULL);
}
const ll MOD = 1000000007LL;
const ll PRIME = 105943LL;
const ll INF = 1e18;
/****************************CEOI 18 D2 P1 - FIB************************************/
v<int> process(v<int> ord) {
v<int> ret = { 1 };
for (int a : ord) {
for(int i = ret.size()-1; ret.size() > 1 && !is_clockwise(ret[i - 1], ret[i], a); i = ret.size()-1)
ret.pop_back();
ret.push_back(a);
}
return ret;
}
int bac(v<int> &A) {
return A[A.size() - 1];
}
int bac1(v<int> &A) {
return A[A.size() - 2];
}
void merge(v<int> &A, v<int> &B) {
A.pop_back();
while (1) {
int c = 0;
while (B.size() > 1 && !is_clockwise(bac(A), bac(B), bac1(B))) {
B.pop_back();
c++;
}
while (A.size() > 1 && !is_clockwise(bac1(A), bac(A), bac(B))) {
A.pop_back();
c++;
}
if (c == 0) break;
}
}
int main() {
io();
int N = get_n();
v<int> pnts[2] = { {2}, {2} };
FORE(i, 3, N)
pnts[is_clockwise(1, 2, i)].push_back(i);
FOR(h, 0, 2) {
sort(all(pnts[h]), [&](const int &a, const int &b) {return is_clockwise(1, a, b); });
pnts[h] = process(pnts[h]);
}
//darr(pnts[0], pnts[0].size());
//darr(pnts[1], pnts[1].size());
reverse(all(pnts[1]));
pnts[1].insert(pnts[1].begin(), pnts[1].back());
pnts[1].pop_back();
merge(pnts[0], pnts[1]);
// darr(pnts[0], pnts[0].size());
// darr(pnts[1], pnts[1].size());
reverse(all(pnts[0]));
reverse(all(pnts[1]));
merge(pnts[1], pnts[0]);
// darr(pnts[0], pnts[0].size());
// darr(pnts[1], pnts[1].size());
give_answer(pnts[0].size()+pnts[1].size());
return 0;
}
