#include <bits/stdc++.h>
using namespace std;
int a[1100], b[1100];
int main() {
  int N, M, x, y;
  cin >> N >> M;
  while (M--) {
    cin >> x >> y;
    a[x] = 1;
    b[y] = 1;
  }
  int i, ans = 0;
  for (i = 2; i <= N / 2; i++) {
    ans += !a[i] + !a[N + 1 - i] + !b[i] + !b[N + 1 - i];
  }
  if (N & 1) {
    ans += !a[N + 1 >> 1] || !b[N + 1 >> 1];
  }
  cout << ans << endl;
}
