#include <bits/stdc++.h>
using namespace std;
const int MAXN = 1000 * 1 + 10, INF = 1e9 + 10;
bool col[MAXN], row[MAXN], mark[MAXN][5];
int main() {
  ios::sync_with_stdio(false);
  int n, m;
  cin >> n >> m;
  for (int i = 0; i < m; i++) {
    int x, y;
    cin >> x >> y;
    row[x] = true;
    col[y] = true;
  }
  int ans = 0;
  for (int i = 2; i < n; i++) {
    if (n % 2 && i == (n + 1) / 2) {
      if (!col[i] || !row[i]) ans++;
      continue;
    }
    if (!col[i]) ans++;
    if (!row[i]) ans++;
  }
  cout << ans << endl;
  return 0;
}
