#include <bits/stdc++.h>
using namespace std;
const int M = 1e9 + 7;
int V, E, i, j, k, u, v, x, y, p, q, r, t, n, m;
vector<int> *g;
vector<bool> sn;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cin >> n >> m;
  vector<bool> ha(n + 1, true);
  vector<bool> va(n + 1, true);
  while (m--) {
    cin >> x >> y;
    ha[x] = false;
    va[y] = false;
  }
  int cnt = 0;
  for (int i = 2; i <= n - 1; i++) {
    if (ha[i]) cnt++;
  }
  for (int i = 2; i <= n - 1; i++) {
    if (ha[i] && i == n - i + 1) continue;
    if (va[i]) cnt++;
  }
  cout << cnt << "\n";
}
