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