#include <bits/stdc++.h>
using namespace std;
int a[2000], b[2000], t1, t2, n, m, patha[2000][5], pathb[2000][5];
int main() {
  cin >> n >> m;
  a[1] = 1;
  a[n] = 1;
  b[1] = 1;
  b[n] = 1;
  for (int i = 1; i <= m; i++) {
    cin >> t1 >> t2;
    a[t1] = 1;
    b[t2] = 1;
  }
  int suma = 0, sumb = 0;
  for (int i = 1; i <= n; i++) {
    if (a[i] == 0) suma++;
    if (b[i] == 0) sumb++;
  }
  cout << suma + sumb -
              ((n % 2) & (a[(n + 1) / 2] == 0) & (b[(n + 1) / 2] == 0))
       << endl;
  return 0;
}
