#include <bits/stdc++.h>
using namespace std;
bool r[1010], c[1010];
int main() {
  int n, m;
  cin >> n >> m;
  for (int i = 0; i < m; i++) {
    int a, b;
    cin >> a >> b;
    a--;
    b--;
    r[a] = 1;
    c[b] = 1;
  }
  int ans = 0;
  for (int i = 1; i < n - 1; i++) {
    if (!c[i]) ans++;
    if (!r[i]) ans++;
    if (!c[i] && !r[i] && !c[n - i] && !r[n - i] && (n - 1 - i) == i) ans--;
  }
  cout << ans << endl;
}
