/*
_____
.' '.
/ 0 0 \
| ^ |
| \ / |
\ '---' /
'._____.'
*/
#pragma GCC optimize ("O3")
#pragma GCC target ("sse4")
#include "trilib.h"
#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/rope>
using namespace std;
using namespace __gnu_pbds;
using namespace __gnu_cxx;
template<typename T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
random_device(rd);
mt19937 rng(rd());
template<class T>
void readi(T &x)
{
T input = 0;
bool negative = false;
char c = ' ';
while (c < '-')
{
c = getchar();
}
if (c == '-')
{
negative = true;
c = getchar();
}
while (c >= '0')
{
input = input * 10 + (c - '0');
c = getchar();
}
if (negative)
{
input = -input;
}
x = input;
}
template<class T>
void printi(T output)
{
if (output == 0)
{
putchar('0');
return;
}
if (output < 0)
{
putchar('-');
output = -output;
}
int aout[20];
int ilen = 0;
while(output)
{
aout[ilen] = ((output % 10));
output /= 10;
ilen++;
}
for (int i = ilen - 1; i >= 0; i--)
{
putchar(aout[i] + '0');
}
return;
}
template<class T>
void ckmin(T &a, T b)
{
a = min(a, b);
}
template<class T>
void ckmax(T &a, T b)
{
a = max(a, b);
}
long long expo(long long a, long long e, long long mod)
{
return ((e == 0) ? 1 : ((expo(a * a % mod, e >> 1, mod)) * ((e & 1) ? a : 1) % mod));
}
template<class T, class U>
T nmod(T &x, U mod)
{
if (x >= mod) x -= mod;
}
template<class T>
T gcd(T a, T b)
{
return (b ? gcd(b, a % b) : a);
}
template<class T>
T randomize(T mod)
{
return (uniform_int_distribution<T>(0, mod - 1))(rng);
}
#define y0 ___y0
#define y1 ___y1
#define MP make_pair
#define MT make_tuple
#define PB push_back
#define PF push_front
#define LB lower_bound
#define UB upper_bound
#define fi first
#define se second
#define debug(x) cerr << #x << " = " << x << endl;
#define sz(x) ((int) (x.size()))
const long double PI = 4.0 * atan(1.0);
const long double EPS = 1e-9;
#define MAGIC 347
#define SINF 10007
#define CO 1000007
#define INF 1000000007
#define BIG 1000000931
#define LARGE 1696969696967ll
#define GIANT 2564008813937411ll
#define LLINF 2696969696969696969ll
#define MAXN 40013
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<ld, ld> pdd;
int N, Q;
rope<int> hull;
int ans;
map<int, bool> mp[MAXN];
bool ccw(int u, int v, int w)
{
int x = u, y = v, z = w;
if (v < u && v < w)
{
u = y; v = z; w = x;
}
else if (w < u && w < v)
{
u = z; v = x; w = y;
}
if (mp[u].find(v * N + w) != mp[u].end())
{
return mp[u][v * N + w];
}
Q++;
// if (Q == 1000001) assert(false);
bool res = !(is_clockwise(u + 1, v + 1, w + 1));
mp[u][v * N + w] = res; mp[u][w * N + v] = !res;
return res;
}
int fetch(int idx)
{
return hull[(idx + hull.size()) % hull.size()];
}
void debug_hull()
{
cerr << "hull has:";
for (int x : hull)
{
cerr << ' ' << x;
}
cerr << endl;
}
int32_t main()
{
ios_base::sync_with_stdio(0);
// cout << fixed << setprecision(10);
// cerr << fixed << setprecision(10);
// freopen ("file.in", "r", stdin);
// freopen ("file.out", "w", stdout);
N = get_n();
for (int i = 0; i < N; i++)
{
// cerr << "before " << i << ' ';
// debug_hull();
if (hull.size() < 2)
{
hull.PB(i);
continue;
}
if (hull.size() == 2)
{
int u = hull[0], v = hull[1];
if (ccw(u, v, i))
{
hull.PB(i);
}
else
{
hull.insert(1, i);
}
continue;
}
int lo = 0, hi = hull.size() - 1;
//find the last guy such that (0, i, )
while(hi > lo)
{
int mid = (lo + hi + 1) / 2, idx = fetch(mid);
if (ccw(0, idx, i))
{
lo = mid;
}
else
{
hi = mid - 1;
}
}
//ccw(0, idx, i!)
int idx = lo;
while(true)
{
if (hull.size() < 2)
{
break;
}
if (!ccw(fetch(idx - 1), fetch(idx), i))
{
hull.erase(idx);
idx--;
if (idx < 0) idx == hull.size() - 1;
continue;
}
else if (!ccw(i, fetch(idx + 1), fetch(idx + 2)))
{
hull.erase((idx + 1) % hull.size());
continue;
}
else
{
break;
}
}
if (ccw(fetch(idx), i, fetch(idx + 1)))
{
hull.insert(idx + 1, i);
}
}
// debug_hull();
ans = hull.size();
give_answer(ans);
// cerr << "time elapsed = " << (clock() / (CLOCKS_PER_SEC / 1000)) << " ms" << endl;
return 0;
}
