#include "trilib.h"
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int n;
int ccw(int x, int y, int z){
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=1;i<=n;i++) if (check_hull(i)) build_hull(i);
printf("FUCK\n");
return 0;
}
