#include <bits/stdc++.h>
using namespace std;
int row[1008], col[1008], n, m, a, b, cnt;
int main() {
  cin >> n >> m;
  for (int i = 0; i < n + 1; i++) row[i] = col[i] = true;
  while (m--) {
    cin >> a >> b;
    row[a] = col[b] = false;
  }
  for (int i = 2; i < n; i++) cnt += (row[i] + col[i]);
  if (n % 2) cnt -= (row[n / 2 + 1] && col[n / 2 + 1]);
  cout << cnt << endl;
  return 0;
}
