#include "bits/stdc++.h"
using namespace std;

#define ll long long
#define MOD ((int) (1e9) + 7)
#define pii pair<int, int>

#define N 2010

typedef pair<pii, int> pt;

pii vectorize(pii A, pii B) {
    return pii(B.first - A.first, B.second - A.second);
}

ll cross(pii v0, pii v1) {
    return 1ll * v0.first * v1.second - 1ll * v0.second * v1.first;
}

void polar_sort(vector<pt>& arr, pii center) {
    sort(arr.begin(), arr.end(), [&](pt a, pt b) {
        auto v0 = vectorize(center, a.first);
        auto v1 = vectorize(center, b.first);
        return atan2(v0.second, v0.first) < atan2(v1.second, v1.first);        
    });
}

pt stk[N];
int nxt[N], onhull[N];

int main() {
#ifdef TEST
    freopen("zz.in", "r+", stdin);
#endif
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    int n; cin >> n;
    vector<pt> pts(n);
    for (int i = 0; i < n; ++ i) {
        int x, y; cin >> x >> y;
        pts[i] = pt(pii(x, y), i);
    }

    sort(pts.begin(), pts.end());
    polar_sort(pts, pts[0].first);

    int sz = 0;
    stk[++ sz] = pts[0];
    stk[++ sz] = pts[1];
    for (int i = 2; i < n; ++ i) {
        while (sz >= 2) {
            auto p0 = stk[sz - 1].first;
            auto p1 = stk[sz].first;
            auto p2 = pts[i].first;
            
            if (cross(vectorize(p0, p1), vectorize(p0, p2)) < 0) {
                -- sz;
            } else {
                break;
            }
        }
        stk[++ sz] = pts[i];
    }

    for (int i = 1; i <= sz; ++ i) {
        onhull[stk[i].second] = 1;
        nxt[stk[i].second] = i == sz ? stk[1].second : stk[i+1].second;
    }

    int res = 1;
    vector<pt> ss;
    for (int i = 0; i < n; ++ i) {
        auto [p, id] = pts[i];
        if (onhull[id]) continue;

        ss.clear();
        for (int j = 0; j < n; ++ j) if (pts[j].second != id) ss.emplace_back(pts[j]);
        polar_sort(ss, p);

        int cont = 0;
        for (int j = 0; j < ss.size(); ++ j) {
            int k = j == ss.size()-1 ? 0 : j+1;
            int cont = 1;
            cont &= onhull[ss[j].second];
            cont &= onhull[ss[k].second];
            cont &= nxt[ss[j].second] == ss[k].second || nxt[ss[k].second] == ss[j].second;
            res += cont;
        }
    }

    cout << res << '\n';

    return 0;
}