#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  if (n == 2) {
    cout << 0 << endl;
    return 0;
  }
  vector<bool> row(n - 2, true);
  vector<bool> col(n - 2, true);
  int x, y;
  for (int i = 0; i < m; i++) {
    cin >> x >> y;
    if (x > 1 && x < n) row[x - 2] = false;
    if (y > 1 && y < n) col[y - 2] = false;
  }
  int res = 0;
  for (int i = 0; i < n - 2; i++) {
    if (n % 2 == 1 && i == (n - 2) / 2) {
      res += max(row[i], col[i]);
    } else {
      res += row[i] + col[i];
    }
  }
  cout << res << endl;
  return 0;
}
