#include <bits/stdc++.h>
using namespace std;
#define maxn 1000100
#define ii pair<int, int>
#define vii vector<ii>

bool lazy[4*maxn];
int  st[4*maxn][2];

int left(int x){return 2*x;}
int right(int x){return 2*x+1;}

void build(int id, int l, int r) {
    st[id][1] = 0;
    st[id][0] = r-l+1;
    lazy[id] = 0;
    if (l == r) return;
    int mid = (l+r)/2;
    build(left(id), l, mid);
    build(right(id), mid+1, r);
}

inline void propagate(int id, int l, int r) {
    if (lazy[id]) {
        st[id][1] = st[id][0];
        st[id][0] = 0;
        if (l != r) {
            lazy[left(id)] = true;
            lazy[right(id)] = true;
        }
    }
    lazy[id] = 0;
}

int query(int id, int l, int r, int start, int finish) {
    cout << "qr\n";
    printf("%d %d %d %d %d\n", id, l, r, start, finish);
    propagate(id, l, r);
    if (l > finish || r < start) return 0;
    if (l >= start && r <= finish) return r-l+1 - st[id][0] - st[id][1];
    int mid = (l+r)/2;
    return
        query(left(id), l, mid, start, finish) +
        query(right(id), mid+1, r, start, finish);
}

void update(int id, int l, int r, int start, int finish) {
    // cout << "up\n";
    // assert(min({l, r, start, finish}) >= 0);
    propagate(id, l, r);
    if (l > finish || r < start) return;
    printf("up %d %d %d %d %d\n", id, l, r, start, finish);
    if (l >= start && r <= finish) {
        st[id][1] = st[id][0];
        st[id][0] = 0;
        lazy[left(id)] = true;
        lazy[right(id)] = true;
        return;
    }
    int mid = (l+r)/2;
    update(left(id), l, mid, start, finish);
    update(right(id), mid+1, r, start, finish);
    st[id][0] = st[left(id)][0] + st[right(id)][0];
    st[id][1] = st[left(id)][1] + st[right(id)][1];
}

struct ev {
    int x, y1, y2;
    bool operator < (ev o) {
        if (x != o.x) return x < o.x;
        return y1 < o.y1;
    }
};

vii dots;
int n,x,y;

int ans = 0;
int solve() {
    vector<ev> e;
    for (int i = 0; i <= n; i++) {
        int j = (i+1) % n;
        if (dots[i].first == dots[j].first) {
            e.push_back({dots[i].first, min(dots[i].second, dots[j].second), max(dots[i].second, dots[j].second)});

        }
    }
    int mi = 1e9;
    for (auto u: e)
        mi = min(mi, u.y1);
    for (auto &u: e) {
        u.y1 -= mi-1,
        u.y2 -= mi-1;
    }

    sort(e.begin(), e.end());
    for (auto u: e) {
        ans += query(1, 1, 1000010,u.y1, u.y2);
        update(1, 1, 1000010,u.y1, u.y2);
    }
}

int main(){
    cin >> n;
    for (int i = 0; i < n; ++i) {
        cin >> x >> y;
        dots.push_back({x,y});
    }
    solve();
    for (int i = 0; i , n; ++i) {
        x = dots[i].first;
        y = dots[i].second;
        dots[i] = {-y, x};
    }
    solve();
    cout << ans << '\n';

    return 0;
}