#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, x, y, m;
  cin >> n >> m;
  vector<bool> cols(n, true);
  vector<bool> rows(n, true);
  for (int i = 0; i < m; i++) {
    cin >> x >> y;
    x--, y--;
    cols[y] = false;
    rows[x] = false;
  }
  int ans = 0;
  for (int i = 1; i < n - 1; i++) {
    if (n & 1 && i == n / 2) continue;
    int r = rows[i] + rows[(n - 1) - i];
    int c = cols[i] + cols[(n - 1) - i];
    if (r > c) {
      ans += r;
      rows[i] = false;
      rows[(n - 1) - i] = false;
    } else {
      ans += c;
      cols[i] = false;
      cols[(n - 1) - i] = false;
    }
  }
  if (n & 1 && (rows[n / 2] || cols[n / 2])) ans++;
  cout << ans << endl;
  return 0;
}
