#include <bits/stdc++.h>
using namespace std;
int main() {
  bool r[1000] = {0}, c[1000] = {0}, opr[1000] = {0}, opc[1000] = {0};
  bool vr[1000] = {0}, vc[1000] = {0}, vopr[1000] = {0}, vopc[1000] = {0};
  int n = 0, m = 0, ans = 0;
  cin >> n >> m;
  for (int i = 2; i < n; i++)
    vr[i] = vc[i] = vopr[i] = vopc[i] = r[i] = c[i] = opr[i] = opc[i] = 1;
  while (m--) {
    int x = 0, y = 0;
    cin >> x >> y;
    vr[x] = vopr[x] = 0;
    vc[y] = vopc[y] = 0;
  }
  for (int i = 2, j = n - 1; i < j; i++, j--) {
    if (vr[i]) ans++, vr[i] = 0;
    if (vopc[i]) ans++, vopc[i] = 0;
    if (vopr[j]) ans++, vopr[j] = 0;
    if (vc[j]) ans++, vc[j] = 0;
  }
  if (n % 2 &&
      (vr[n / 2 + 1] || vc[n / 2 + 1] || vopc[n / 2 + 1] || vopr[n / 2 + 1]))
    ans++;
  cout << ans;
  return 0;
}
