#include <bits/stdc++.h>
using namespace std;
bool hang[1005], lie[1005];
int main() {
  int i, n, m, x, y;
  scanf("%d%d", &n, &m);
  memset(hang, 0, sizeof(hang));
  memset(lie, 0, sizeof(lie));
  for (i = 0; i < m; ++i) {
    scanf("%d%d", &x, &y);
    hang[x] = 1;
    lie[y] = 1;
  }
  int ans = 0;
  for (i = 2; i < n; ++i) {
    if (!hang[i]) ans++;
    if (!lie[i]) ans++;
  }
  if (n % 2 && !hang[n / 2 + 1] && !lie[n / 2 + 1]) ans--;
  cout << ans << endl;
  return 0;
}
