#include <bits/stdc++.h>
using namespace std;
const int N = 3e5 + 1;
int n, m, ans;
bool xa[N], ya[N];
int main() {
  cin >> n >> m;
  for (int i = 0; i < m; ++i) {
    int x, y;
    cin >> x >> y;
    xa[x] = ya[y] = 1;
  }
  for (int i = 2; i < n; ++i) {
    if (!xa[i]) ans++;
    if (!ya[i]) ans++;
  }
  if (n % 2 && !xa[(n + 1) / 2] && !ya[(n + 1) / 2]) ans--;
  cout << ans;
  return 0;
}
