#include <bits/stdc++.h>
using namespace std;
int main() {
  {
    ios::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
  };
  int n, m;
  cin >> n >> m;
  vector<int> x(n), y(n);
  while (m--) {
    int a, b;
    cin >> a >> b;
    a--;
    b--;
    x[a] = 1;
    y[b] = 1;
  }
  int count = 0;
  for (int i = 1; i < n - 1; i++) {
    if (x[i] == 0 && y[i] == 0) {
      if (n % 2 != 1 || i != n / 2)
        count += 2;
      else
        count++;
    } else if (x[i] == 1 && y[i] == 1)
      continue;
    else
      count++;
  }
  cout << count << endl;
  return 0;
}
