#include <bits/stdc++.h>
#include "trilib.h"
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const int MAXN = 40000;
int N, p, q;
vector<int> A, B, D, C;
bool ccw(int a, int b, int c) { return !is_clockwise(a, b, c); }
int main()
{
int i, j;
N=get_n();
for(i=3; i<=N; i++)
{
if(ccw(1, 2, i)) A.push_back(i);
else B.push_back(i);
}
A.push_back(2); B.push_back(2);
sort(A.begin(), A.end(), [&](const int &p, const int &q) { return ccw(1, p, q); });
sort(B.begin(), B.end(), [&](const int &p, const int &q) { return !ccw(1, p, q); });
A.insert(A.begin(), 1);
B.insert(B.begin(), 1);
vector<int> S;
for(auto it : A)
{
while(S.size()>1 && !ccw(S[S.size()-2], S[S.size()-1], it)) S.pop_back();
S.push_back(it);
}
A=S; S.clear();
for(auto it : B)
{
while(S.size()>1 && ccw(S[S.size()-2], S[S.size()-1], it)) S.pop_back();
S.push_back(it);
}
B=S; S.clear();
A.erase(A.begin()); A.erase(A.begin());
B.erase(B.begin()); B.erase(B.begin());
//for(auto it : A) printf("%d ", it); printf("\n");
//for(auto it : B) printf("%d ", it); printf("\n");
vector<int> T;
T=A; reverse(T.begin(), T.end()); T.push_back(2);
for(i=0; i<B.size(); i++) while(T.size()>1 && !ccw(B[i], T[T.size()-1], T[T.size()-2])) D.push_back(T.back()), T.pop_back();
T.clear();
T=B; reverse(T.begin(), T.end()); T.push_back(2);
for(i=0; i<A.size(); i++) while(T.size()>1 && ccw(A[i], T[T.size()-1], T[T.size()-2])) D.push_back(T.back()), T.pop_back();
T.clear();
T=A; T.push_back(1);
for(i=B.size()-1; i>=0; i--) while(T.size()>1 && ccw(B[i], T[T.size()-1], T[T.size()-2])) D.push_back(T.back()), T.pop_back();
T.clear();
T=B; T.push_back(1);
for(i=A.size()-1; i>=0; i--) while(T.size()>1 && !ccw(A[i], T[T.size()-1], T[T.size()-2])) D.push_back(T.back()), T.pop_back();
T.clear();
sort(D.begin(), D.end());
D.erase(unique(D.begin(), D.end()), D.end());
C.push_back(1); C.push_back(2);
for(auto it : A) C.push_back(it);
for(auto it : B) C.push_back(it);
int ans=0;
for(auto it : C) if(!binary_search(D.begin(), D.end(), it)) ans++;
printf("%d", ans);
}
