#include <bits/stdc++.h>
using namespace std;
int n, m;
set<int> first, second;
set<int>::iterator it;
int a, b;
bool cx[1010], cy[1010];
int main() {
  cin >> n >> m;
  for (int i = 0; i < m; i++) {
    cin >> a >> b;
    first.insert(a);
    second.insert(b);
  }
  for (it = first.begin(); it != first.end(); it++) cx[*it] = 1;
  for (it = second.begin(); it != second.end(); it++) cy[*it] = 1;
  int ans = 0;
  for (int i = 2; i < n; i++) {
    if (n % 2 && i == n / 2 + 1) {
      if (!cx[i] || !cy[i]) ans++;
    } else {
      if (!cx[i]) ans++;
      if (!cy[i]) ans++;
    }
  }
  cout << ans;
  return 0;
}
