#include <bits/stdc++.h>
using namespace std;
int x, y;
int row[100003], col[100003];
bool counted[100003];
bool flag = false;
int counter, rows, cols, counter2;
int main() {
  int n, m;
  cin >> n >> m;
  for (int i = 0; i < m; i++) {
    scanf("%d %d", &x, &y);
    row[x] = 1;
    col[y] = 1;
  }
  for (int i = 2; i < n; i++) {
    if (n % 2 == 0 || i != (n / 2 + 1)) {
      if (row[i] == 0) counter++;
      if (col[i] == 0) counter++;
    }
  }
  if (n % 2 != 0) {
    if ((col[n / 2 + 1] != 0 && row[n / 2 + 1] == 0) ||
        (col[n / 2 + 1] == 0 && row[n / 2 + 1] != 0) ||
        (col[n / 2 + 1] == 0 && row[n / 2 + 1] == 0))
      counter++;
  }
  cout << max(counter, 0);
  return 0;
}
