#include <bits/stdc++.h>
using namespace std;
void debug_out() { cerr << endl; }
template <class T>
ostream& prnt(ostream& out, T v) {
  out << v.size() << '\n';
  for (auto e : v) out << e << ' ';
  return out;
}
template <class T>
ostream& operator<<(ostream& out, vector<T> v) {
  return prnt(out, v);
}
template <class T>
ostream& operator<<(ostream& out, set<T> v) {
  return prnt(out, v);
}
template <class T1, class T2>
ostream& operator<<(ostream& out, map<T1, T2> v) {
  return prnt(out, v);
}
template <class T1, class T2>
ostream& operator<<(ostream& out, pair<T1, T2> p) {
  return out << '(' << p.st << ' ' << p.nd << ')';
}
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << H;
  debug_out(T...);
}
const long double PI = acos(-1);
int n, m, L[100005], C[100005], nr;
pair<int, int> v[100005];
int main() {
  ios::sync_with_stdio(false);
  cin >> n >> m;
  for (int i = 1; i <= m; i++) {
    cin >> v[i].first >> v[i].second;
    L[v[i].first] = 1;
    C[v[i].second] = 1;
  }
  for (int i = 2; i < n; i++) {
    if (!L[i]) nr++;
    if (!C[i]) nr++;
  }
  if (n % 2 == 1 && !L[n / 2 + 1] && !C[n / 2 + 1]) nr--;
  cout << nr << '\n';
  return 0;
}
