#include <bits/stdc++.h>
using namespace std;
int r[1001], c[1001];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int n, m, cnt = 0;
  cin >> n >> m;
  for (int i = 1; i <= m; i++) {
    int x, y;
    cin >> x >> y;
    r[x] = 1;
    c[y] = 1;
  }
  for (int i = 2; i < n; i++) {
    if (r[i] == 0) cnt++;
    if (c[i] == 0) cnt++;
  }
  if (n % 2 != 0 && r[(n + 1) / 2] == 0 && c[(n + 1) / 2] == 0) cnt--;
  cout << cnt;
}
