#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  int r[1001] = {0}, c[1001] = {0}, a, b;
  for (int i = 0; i < m; i++) {
    cin >> a >> b;
    r[a] = 1;
    c[b] = 1;
  }
  int co = 0;
  for (int i = 2; i < n; i++) {
    if (r[i] == 0) co++;
    if (c[i] == 0) co++;
  }
  if (n % 2 != 0 && c[(n / 2) + 1] == 0 && r[(n / 2) + 1] == 0) co--;
  cout << co << endl;
  return 0;
}
