#include <bits/stdc++.h>
using namespace std;
int nod(int x, int y) {
  if (x)
    return nod(y % x, x);
  else
    return y;
}
long long nok(long long x, long long y) { return x / nod(x, y) * y; }
int main() {
  ios_base ::sync_with_stdio(false);
  cin.tie(NULL);
  int n, m, i, a[1234] = {0}, b[1234] = {0}, ans = 0, x, y;
  cin >> n >> m;
  for (i = 0; i < m; i++) {
    cin >> x >> y;
    a[x] = -1;
    b[y] = -1;
  }
  for (i = 2; i <= (n + 1) / 2; i++) {
    if (a[i] != -1) ans++;
    if (a[n - i + 1] != -1 && i != n - i + 1) ans++;
  }
  for (i = 2; i < n; i++)
    if (b[i] != -1 && (i != n - i + 1 || (i == n - i + 1 && a[i] == -1))) ans++;
  cout << ans;
}
