#include <bits/stdc++.h>
using namespace std;
#ifndef LOCAL
#include "trilib.h"
#else
const int N = 40010;
int _n;
long long x[N], y[N];
int get_n() {
cin >> _n;
for(int i = 1; i <= _n; ++i) {
cin >> x[i] >> y[i];
}
return _n;
}
int is_clockwise(int a, int b, int c) {
assert(1 <= a && a <= _n && 1 <= b && b <= _n && 1 <= c && c <= _n && a != b && b != c && c != a);
return (x[b] - x[a]) * (y[c] - y[a]) - (y[b] -y[a]) * (x[c] - x[a]) < 0;
}
void give_answer(int s) {
cout << s << endl;
exit(0);
}
#endif
vector<int> convex(vector<int> p) {
sort(p.begin() + 1, p.end(), [](int i, int j) {
return !is_clockwise(1, i, j);
});
vector<int> hull = { p[0] };
for(int i = 1; i < p.size(); ++i) {
int sz = hull.size();
while(sz > 1 && is_clockwise(hull[sz - 2], hull[sz - 1], p[i]))
hull.pop_back(), --sz;
hull.push_back(p[i]);
}
return hull;
}
vector<int> hull[2];
void fix_back() {
hull[1].pop_back();
while(1) {
int sz = hull[0].size(), found = 0;
if(sz > 1 && is_clockwise(hull[0][sz - 2], hull[0].back(), hull[1].back())) {
hull[0].pop_back();
found = 1;
}
sz = hull[1].size();
if(sz > 1 && is_clockwise(hull[0].back(), hull[1].back(), hull[1][sz - 2])) {
hull[1].pop_back();
found = 1;
}
if(!found) return;
}
}
int main(int argc, char const *argv[]) {
#ifdef LOCAL
freopen("in", "r", stdin);
#endif
int n = get_n();
hull[0] = hull[1] = {1, 2};
for(int i = 3; i <= n; ++i) {
hull[!is_clockwise(1, 2, i)].push_back(i);
}
hull[0] = convex(hull[0]);
hull[1] = convex(hull[1]);
hull[1].push_back(1);
reverse(hull[1].begin(), hull[1].end());
hull[1].pop_back();
fix_back();
reverse(hull[0].begin(), hull[0].end());
reverse(hull[1].begin(), hull[1].end());
swap(hull[0], hull[1]);
fix_back();
give_answer(hull[0].size() + hull[1].size());
}
