#include <bits/stdc++.h>
using namespace std;
set<int> row, col;
int n, m;
int main() {
  cin >> n >> m;
  for (int i = 2; i <= n - 1; i++) {
    row.insert(i);
    col.insert(i);
  }
  for (int i = 1; i <= m; i++) {
    int x, y;
    cin >> x >> y;
    if (row.find(x) != row.end()) row.erase(x);
    if (col.find(y) != col.end()) col.erase(y);
  }
  int ans = row.size() + col.size();
  if (n % 2 && row.find((n + 1) / 2) != row.end() &&
      col.find((n + 1) / 2) != col.end())
    ans--;
  cout << ans;
  return 0;
}
