#include <bits/stdc++.h>
using namespace std;
bool arr[1020][1020];
bool visited[1020];
int main() {
  memset(arr, false, sizeof(arr));
  memset(visited, false, sizeof(visited));
  int n, m;
  cin >> n >> m;
  int a, b;
  for (int i = 0; i < m; i++) {
    cin >> a >> b;
    arr[a - 1][b - 1] = true;
  }
  int ct = 0;
  for (int i = 1; i < n - 1; i++) {
    bool check = true;
    for (int j = 0; j < n; j++)
      if (arr[i][j]) {
        check = false;
        break;
      }
    if (check) {
      visited[i] = true;
      ct++;
    }
  }
  for (int i = 1; i < n - 1; i++) {
    bool check = true;
    for (int j = 0; j < n; j++)
      if (arr[j][i]) {
        check = false;
        break;
      }
    if (check) {
      if (!visited[i] || !visited[n - 1 - i])
        ct++;
      else if (visited[n - 1 - i]) {
        if ((n % 2 == 0) || (i != (n / 2))) ct++;
      } else if (visited[i]) {
        if ((n % 2 == 0) || (i != (n / 2))) ct++;
      }
    }
  }
  cout << ct << endl;
  return 0;
}
