#include <bits/stdc++.h>
#include "trilib.h"
using namespace std;
// macros
typedef long long ll;
typedef long double ld;
typedef pair<int, int> ii;
typedef pair<ll, ll> lll;
typedef tuple<int, int, int> iii;
typedef vector<int> vi;
typedef vector<ii> vii;
typedef vector<iii> viii;
typedef vector<ll> vll;
typedef vector<lll> vlll;
#define REP(a,b,c) for(int a=int(b); a<int(c); a++)
#define RE(a,c) REP(a,0,c)
#define RE1(a,c) REP(a,1,c+1)
#define REI(a,b,c) REP(a,b,c+1)
#define REV(a,b,c) for(int a=int(c-1); a>=int(b); a--)
#define FOR(a,b) for(auto& a : b)
#define all(a) a.begin(), a.end()
#define INF 1e9
#define EPS 1e-9
#define pb push_back
#define popb pop_back
#define fi first
#define se second
#define sz size()
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
// input
template<class T> void IN(T& x) {cin >> x;}
template<class H, class... T> void IN(H& h, T&... t) {IN(h); IN(t...); }
// output
template<class T1, class T2> void OUT(const pair<T1,T2>& x);
template<class T> void OUT(const T& x) {cout << x;}
template<class H, class... T> void OUT(const H& h, const T&... t) {OUT(h); OUT(t...); }
template<class T1, class T2> void OUT(const pair<T1,T2>& x) {OUT(x.fi," ",x.se);}
template<class... T> void OUTL(const T&... t) {OUT(t..., "\n"); }
//===================//
// Added libraries //
//===================//
//===================//
//end added libraries//
//===================//
void program();
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
program();
}
//===================//
// begin program //
//===================//
const int MX = 50000;
int n, m;
int SHUF[MX];
bool cw(int x, int y, int z) {
return is_clockwise(SHUF[x],SHUF[y],SHUF[z]);
}
bool ccw(int x, int y, int z) {
return !is_clockwise(SHUF[x],SHUF[y],SHUF[z]);
}
vi getOnSide(vi& pos, int x, int y, bool side) {
vi ret;
FOR(i,pos) {
if(x == i || y == i) continue;
if(cw(x,y,i) == side) ret.pb(i);
}
return ret;
}
int MEX(int x, int y) {
RE1(i,3)
if(x != i && y != i) return i;
}
bool isBeg(int i) {
int mostCW = MEX(i,0);
RE1(j,n) {
if(j == i) continue;
if(j == mostCW) continue;
if(cw(i,mostCW,j)) mostCW = j;
}
RE1(j,n) {
if(j == i) continue;
if(j == mostCW) continue;
if(cw(i,mostCW,j)) return 0;
}
return 1;
}
int origin, or2;
int S[MX], C[MX];
void program() {
n = get_n();
RE1(i,n) SHUF[i] = i;
shuffle(SHUF+1,SHUF+n+1,rng);
if(n == 3) {
give_answer(3);
return;
}
origin = 1;
if(!isBeg(origin)) origin = 2;
RE(i,n) S[i] = i+1;
RE(i,n) if(S[i] == origin) swap(S[i], S[0]);
or2 = MEX(origin,0);
sort(S+1,S+n,[](int i, int j) {
if(i == or2) return (bool)1;
if(j == or2) return (bool)0;
bool ccwi = ccw(origin,or2,i);
bool ccwj = ccw(origin,or2,j);
if(ccwi == ccwj)
return cw(origin, i, j);
return ccwi;
});
if(isBeg(origin)) {
m=0;
C[m++] = S[n-1], C[m++] = S[0];
int i=1;
while(i < n) {
if(ccw(C[m-2],C[m-1],S[i])) C[m++] = S[i++];
else m--;
}
give_answer(m-1);
} else {
m=0;
C[m++] = S[n-1], C[m++] = S[0];
int i=1;
S[n++] = S[or2];
while(i < n) {
if(ccw(C[m-2],C[m-1],S[i])) C[m++] = S[i++];
else m--;
}
give_answer(m-2);
}
}
