#include "trilib.h"
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
constexpr int ITER = 2;
int n, cnt[100100], qcnt;
int ccw(int x, int y, int z){
qcnt++;
assert(qcnt <= 1000000);
return is_clockwise(x, y, z)?-1:1;
}
bool check_hull(int s){
int L, R;
L = R = (s==1)?2:1;
for (int i=1;i<=n;i++) if (i!=s && i!=L){
if (ccw(s, L, i)==1) L = i;
else if (ccw(s, R, i)==-1) R = i;
//printf("%d: L = %d R = %d\n", s, L, R);
if (ccw(s, L, R)==1) return 0;
}
return 1;
}
int O;
bool cmp(int x, int y){
return ccw(O, x, y)==1;
}
void build_hull(int s){
O = s;
vector<int> P, hull;
for (int i=1;i<=n;i++) if (i!=s) P.push_back(i);
sort(P.begin(), P.end(), cmp);
hull.push_back(s);
for (auto &x:P){
while(hull.size()>=2 && ccw(*++hull.rbegin(), hull.back(), x)==-1) hull.pop_back();
hull.push_back(x);
}
give_answer(hull.size());
exit(0);
}
int main(){
n = get_n();
for (int i=3;i<=3;i++) if (check_hull(i)) build_hull(i);
O = 3;
vector<int> upper, lower;
upper.push_back(1);
for (int i=2;i<=n;i++) if (i!=O){
if (ccw(O, 1, i) > 0) upper.push_back(i);
else lower.push_back(i);
}
sort(upper.begin(), upper.end(), cmp);
sort(lower.begin(), lower.end(), cmp);
vector<int> P = upper, hull;
for (auto &x:lower) P.push_back(x);
for (int z=0;z<ITER;z++){
for (auto &x:P){
while(hull.size()>=2 && ccw(*++hull.rbegin(), hull.back(), x)==-1) hull.pop_back();
hull.push_back(x);
}
}
for (auto &x:hull) cnt[x]++;
int ans = 0;
for (int i=1;i<=n;i++) if (cnt[i]==ITER) ans++;
give_answer(ans);
return 0;
}
