#include <bits/stdc++.h>
using namespace std;
int main() {
  bool a[1000], b[1000];
  int n, m, x, y;
  cin >> n >> m;
  for (int i(0); i < n; i++) {
    a[i] = 1;
    b[i] = 1;
  }
  for (int i(0); i < m; i++) {
    cin >> x >> y;
    a[x - 1] = 0;
    b[y - 1] = 0;
  }
  unsigned long long t(0);
  if (n % 2 == 1 && m == 0) t--;
  for (int i(1); i < n - 1; i++) {
    if (a[i]) t++;
    if (b[i]) t++;
  }
  cout << t;
}
