#include <bits/stdc++.h>
using namespace std;
int col[2000], row[2000];
int main() {
  int n, m, ans = 0;
  scanf("%d%d", &n, &m);
  for (int i = 1; i <= n; i++) row[i] = 1, col[i] = 1;
  for (int i = 1; i <= m; i++) {
    int x, y;
    scanf("%d%d", &x, &y);
    row[x] = col[y] = 0;
  }
  if (n % 2 && (row[n / 2 + 1] || col[n / 2 + 1])) ans++;
  for (int i = 2; i <= n / 2; i++) {
    ans += row[i] + col[i] + row[n - i + 1] + col[n - i + 1];
  }
  printf("%d", ans);
  return 0;
}
