#include <bits/stdc++.h>
using namespace std;
const int N = 1010;
int r[N], c[N], n, m;
int main() {
  cin >> n >> m;
  r[0] = r[n - 1] = c[0] = c[n - 1] = 1;
  for (int i = 0; i < m; i++) {
    int x, y;
    cin >> x >> y;
    r[x - 1] = 1;
    c[y - 1] = 1;
  }
  int res = 2 * n;
  for (int i = 0; i < n; i++) res -= r[i] + c[i];
  if (n % 2 == 1 && r[n / 2] == 0 && c[n / 2] == 0) --res;
  cout << res << endl;
  return 0;
}
