#include <bits/stdc++.h>
using namespace std;
signed main() {
  ios_base::sync_with_stdio(0), cin.tie(0);
  long long n, m;
  cin >> n >> m;
  long long row[n + 1], col[n + 1];
  for (long long i = 1; i < n + 1; i++) row[i] = -1, col[i] = -1;
  for (long long i = 0; i < m; i++) {
    long long x, y;
    cin >> x >> y;
    row[x] = max(row[x], y);
    col[y] = max(col[y], x);
  }
  long long ans = 0;
  for (long long i = 2; i <= (n + 1) / 2; i++) {
    if (i != n + 1 - i) {
      if (row[i] == -1) ans++;
      if (row[n + 1 - i] == -1) ans++;
      if (col[i] == -1) ans++;
      if (col[n + 1 - i] == -1) ans++;
    } else {
      if (row[i] == -1)
        ans++;
      else if (col[i] == -1)
        ans++;
    }
  }
  cout << ans;
}
