#include <bits/stdc++.h>
using namespace std;
int r[1100], c[1100];
int n, m;
int main() {
  cin >> n >> m;
  for (int i = 0; i < n; i++) r[i] = c[i] = 1;
  int ans = 0;
  for (int i = 0; i < m; i++) {
    int a, b;
    scanf("%d%d", &a, &b);
    r[--a] = c[--b] = 0;
  }
  for (int i = 1; i < n / 2; i++) {
    int sum = r[i] + c[i] + r[n - 1 - i] + c[n - 1 - i];
    ans += sum;
  }
  if (n % 2 == 1)
    if (r[n / 2] || c[n / 2]) ans++;
  cout << ans << endl;
  return 0;
}
