#include <bits/stdc++.h>
using namespace std;
int x[1003], y[1003];
int main() {
  ios::sync_with_stdio(false);
  cout.tie(0);
  cin.tie(0);
  int n, m;
  cin >> n >> m;
  int i;
  int a;
  for (i = 0; i < m; i++) {
    cin >> a;
    x[a] = -1;
    cin >> a;
    y[a] = -1;
  }
  int ans = 0;
  for (i = 2; i < n; i++) {
    if (x[i] == -1) ans--;
    if (y[i] == -1) ans--;
  }
  if (n % 2 == 0) {
    ans += (n - 2) * 2;
  } else {
    ans += (n - 3) * 2;
    if (x[(n + 1) / 2] == -1 || y[(n + 1) / 2] == -1) {
      ans += 2;
    } else {
      ans++;
    }
  }
  cout << ans << endl;
}
