#include <bits/stdc++.h>
using namespace std;
int x, y, n, m, a[10000], b[10000], ans;
int main() {
  cin >> n >> m;
  for (int i = 1; i <= m; i++) {
    cin >> x >> y;
    a[x] += 1;
    b[y] += 1;
  }
  for (int i = 2; i <= n - 1; i++) {
    if (a[i] == 0) ans++;
    if (b[i] == 0) ans++;
  }
  if (n % 2 == 1 && a[n / 2 + 1] == b[n / 2 + 1] && a[n / 2 + 1] == 0) ans--;
  cout << ans << endl;
  return 0;
}
