#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  vector<bool> rows(n, true), cols(n, true);
  rows[0] = cols[0] = rows[n - 1] = cols[n - 1] = false;
  while (m--) {
    int i, j;
    cin >> i >> j;
    --i;
    --j;
    rows[i] = false;
    cols[j] = false;
  }
  int ans = count(rows.begin(), rows.end(), true) +
            count(cols.begin(), cols.end(), true);
  if ((n & 1) && rows[n / 2] && cols[n / 2]) --ans;
  cout << ans;
  return 0;
}
