#include <bits/stdc++.h>
using namespace std;
int c[1001], r[1001];
int main() {
  int n, m;
  cin >> n >> m;
  for (int i = 0; i < m; i++) {
    int x, y;
    cin >> x >> y;
    c[y]++;
    r[x]++;
  }
  int k = 1;
  bool s = false;
  long long ans = 0;
  for (int i = 2; i < n; i++) {
    if (c[i] == 0) ans++;
    if (r[i] == 0) ans++;
  }
  if (n % 2 == 1 && c[n / 2 + 1] == 0 && r[n / 2 + 1] == 0) ans -= 1;
  cout << ans << endl;
}
