#include <bits/stdc++.h>
using namespace std;
long long int rowblk[200005];
long long int colblk[200005];
long long int col[200005];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long int l, n, i, j, k, m;
  cin >> n >> m;
  for (i = 1; i <= m; i++) {
    cin >> k >> l;
    rowblk[k] = 1;
    colblk[l] = 1;
  }
  long long int cnt = 0;
  for (i = 2; i < n; i++) {
    if (colblk[i] == 0) {
      cnt++;
      col[i] = 1;
    }
  }
  for (i = 2; i < n; i++) {
    if (rowblk[i] == 0) {
      if (n % 2 != 0 && i == n / 2 + 1) {
        if (col[i] == 0) cnt++;
      } else {
        cnt++;
      }
    }
  }
  cout << cnt << endl;
  return 0;
}
