#include <bits/stdc++.h>
using namespace std;
#define TRACE(x) cerr << #x << " = " << x << endl
#define _ << " _ " <<
#define fi first
#define se second
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef vector<int> vi;
int sign(ll x) {
if (x > 0) return 1;
if (x < 0) return -1;
return 0;
}
int ccw(const pii& a, const pii& b, const pii& c) {
return sign((ll)a.fi * (b.se - c.se) +
(ll)b.fi * (c.se - a.se) +
(ll)c.fi * (a.se - b.se));
}
bool intersect(const pii& a, const pii& b, const pii& c, const pii& d) {
if (a == b || a == c || a == d || b == c || b == d || c == d) return false;
return ccw(a, b, c) != ccw(a, b, d) && ccw(c, d, a) != ccw(c, d, b);
}
int n;
vector<pii> pts;
int ccw(int i, int j, int k) {
return ccw(pts[i], pts[j], pts[k]);
}
bool intersect(int i, int j, int k, int l) {
return intersect(pts[i], pts[j], pts[k], pts[l]);
}
int cmp_center;
bool cmp(int i, int j) {
return ccw(cmp_center, i, j) == 1;
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
cin >> n;
pts.resize(n);
for (auto& it : pts) cin >> it.fi >> it.se;
vector<pii> edges;
set<vi> triangles;
sort(pts.begin(), pts.end());
vector<bool> on_hull(n);
int last = 0;
do {
on_hull[last] = true;
int nxt = 0;
if (last == 0) nxt = 1;
for (int i = 0; i < n; i++)
if (ccw(last, nxt, i) == 1)
nxt = i;
edges.push_back({last, nxt});
if (last != 0 && nxt != 0)
triangles.insert({0, nxt, last});
last = nxt;
} while (last != 0);
for (int i = 0; i < n; i++) {
if (on_hull[i]) continue;
vi tr;
for (auto& it : triangles)
if (ccw(it[0], it[1], i) == 1 &&
ccw(it[1], it[2], i) == 1 &&
ccw(it[2], it[0], i) == 1) {
tr = it;
break;
}
assert(!tr.empty());
triangles.erase(tr);
triangles.insert({tr[0], tr[1], i});
triangles.insert({tr[1], tr[2], i});
triangles.insert({tr[2], tr[0], i});
edges.push_back({i, tr[0]});
edges.push_back({i, tr[1]});
edges.push_back({i, tr[2]});
}
int sol = 0;
for (auto& edg : edges) {
int p = edg.fi, q = edg.se;
vi a, b;
for (int i = 0; i < n; i++) {
if (ccw(p, q, i) == -1) a.push_back(i);
if (ccw(p, q, i) == +1) b.push_back(i);
}
cmp_center = p;
sort(a.begin(), a.end(), cmp);
sort(b.begin(), b.end(), cmp);
vi c = b;
cmp_center = q;
sort(c.begin(), c.end(), cmp);
vi pos(n);
for (int i = 0; i < (int)c.size(); i++) pos[c[i]] = i;
bool ok = true;
int j = 0, k = -1;
for (int i = 0; i < (int)a.size(); i++) {
while (j < (int)b.size() && ccw(a[i], p, b[j]) == -1) {
k = max(k, pos[b[j]]);
j++;
}
if (k != -1)
ok &= !intersect(p, q, a[i], c[k]);
}
if (ok) sol++;
}
cout << sol << '\n';
return 0;
}
