#include <bits/stdc++.h>
using namespace std;
int v1[1005];
int v2[1005];
int main() {
  int n, m;
  memset(v1, 0, sizeof(v1));
  memset(v2, 0, sizeof(v2));
  cin >> n >> m;
  int i;
  int ans = 0;
  int a, b;
  for (i = 0; i < m; i++) {
    scanf("%d%d", &a, &b);
    v1[a] = 1;
    v2[b] = 1;
  }
  if (n % 2 == 0) {
    ans = (n - 2) * 2;
    for (i = 2; i <= n - 1; i++) {
      if (v1[i]) ans--;
      if (v2[i]) ans--;
    }
  } else {
    ans = (n - 3) * 2;
    for (i = 2; i <= n - 1; i++) {
      if (i == (n + 1) / 2) continue;
      if (v1[i]) ans--;
      if (v2[i]) ans--;
    }
    int tmp = (n + 1) / 2;
    if (v1[tmp] == 0 || v2[tmp] == 0) ans++;
  }
  cout << ans << endl;
  return 0;
};
