#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  set<int> xset, yset;
  for (int i = 0; i < m; ++i) {
    int x, y;
    cin >> x >> y;
    if (x > 1 && x < n) {
      xset.insert(x);
    }
    if (y > 1 && y < n) {
      yset.insert(y);
    }
  }
  if (n % 2 != 0 && (xset.find((n + 1) / 2) == xset.end() &&
                     yset.find((n + 1) / 2) == yset.end())) {
    cout << ((n - 2 - xset.size()) + (n - 2 - yset.size() - 1)) << endl;
  } else {
    cout << ((n - 2 - xset.size()) + (n - 2 - yset.size())) << endl;
  }
  return 0;
}
