#include <bits/stdc++.h>
using namespace std;
const int MAXn = 1000 + 17;
int n, m;
bool sotun[MAXn];
bool satr[MAXn];
int main() {
  cin >> n >> m;
  for (int i = 0; i < m; i++) {
    int x, y;
    cin >> x >> y;
    satr[x] = sotun[y] = 1;
  }
  int s = 0;
  for (int i = 2; i <= n / 2; i++) {
    if (satr[i] == 0) s++;
    if (satr[n - i + 1] == 0) s++;
    if (sotun[i] == 0) s++;
    if (sotun[n - i + 1] == 0) s++;
  }
  if (n % 2 == 1) {
    if (satr[n / 2 + 1] == 0 || sotun[n / 2 + 1] == 0) s++;
  }
  cout << s << endl;
  return 0;
}
