#include "trilib.h"
#include <bits/stdc++.h>
using namespace std;
signed main(){
int N = get_n();
vector<int> convex = {1,2,3};
if(!is_clockwise(1,2,3)) swap(convex[1],convex[2]);
for(int n = 4; n <= N; n++){
int len = (int) convex.size();
vector<int> cnt(len,0);
vector<bool> smt(len,0);
for(int i = 0; i < len; i++){
if(!is_clockwise(convex[i],convex[(i+1)%len],n))
cnt[i]++, cnt[(i+1)%len]++, smt[i]=true;
}
vector<int> vec;
bool a = true;
for(int i = 0; i < len; i++) if(cnt[i] != 2){
vec.emplace_back(convex[i]);
if(a && smt[i]){
vec.emplace_back(n); a = false;
}
}
convex.swap(vec);
}
give_answer((int) convex.size());
}
