#include <bits/stdc++.h>
using namespace std;
typedef pair<int, int> pii;
#define fi first
#define se second
#define mp make_pair
#define pb push_back
const int N = 500005;
pii d[N];
bool ok(pii a, pii b, pii c) {
  if (a.fi == b.fi && b.fi == c.fi)
    return false;
  if (a.se == b.se && b.se == c.se)
    return false;
  if (a.fi == b.fi || b.fi == c.fi)
    return true;
  if (a.se == b.se || b.se == c.se)
    return true;
  if (1ll * (a.fi - b.fi) * (b.se - c.se) == 1ll * (b.fi - c.fi) * (a.se - b.se))
    return false;
  return true;
}
int main() {
  int n;
  while (scanf("%d", &n) != EOF) {
    vector<pii> h;
    for (int i = 1; i <= n; i++) {
      scanf("%d%d", &d[i].fi, &d[i].se);
      int u = h.size();
      if (u >= 2 && ok(d[i], h[u - 2], h[u - 1]))
        h.resize(u - 2);
      else
        h.pb(d[i]);
    }
    if (h.size() < 2) {
      printf("%d\n", n % 3);
      return 0;
    }
    int z = 0;
    for (int i = 1; i <= n; i++)
      if (!ok(d[i], h[0], h[1]))
        ++z;
    //printf("n: %d!\n", h.size());
    int u = n - z;
    if (z - u * 2 <= 0) {
      printf("%d\n", n % 3);
      return 0;
    }
    printf("%d\n", z - u * 2);
  }
  return 0;
}