#include <bits/stdc++.h>
#include "trilib.h"
#define mp make_pair
#define X first
#define Y second
#define taskname "Triangle"
using namespace std;
typedef long long ll;
typedef pair <int, int> point;
const int N = 40001;
int _n, ind[N], type[N];
int main(){
_n = get_n();
for(int i = 1; i <= _n; i++)
ind[i] = i;
type[1] = 0;
type[2] = 1;
for(int i = 3; i <= _n; i++)
type[i] = is_clockwise(1, 2, i);
sort(ind + 2, ind + 1 + _n, [](const int &a, const int &b){
bool tA = type[a];
bool tB = type[b];
if (tA != tB)
return tB;
return (!is_clockwise(1, a, b));
});
vector <int> st;
st.push_back(1);
for(int i = 2; i <= _n; i++){
while (st.size() >= 2){
if (is_clockwise(st[st.size() - 2], st[st.size() - 1], ind[i]))
st.pop_back();
else
break;
}
st.push_back(ind[i]);
}
int l = 0, r = st.size() - 1;
while (r - l + 1 > 3){
if (is_clockwise(st[r], st[l], st[l + 1])){
l++;
continue;
}
if (is_clockwise(st[r - 1], st[r], st[l])){
r--;
continue;
}
break;
}
give_answer(r - l + 1);
return 0;
}
