#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  int n, m;
  cin >> n >> m;
  int a[1002];
  int b[1002];
  fill(a + 1, a + 1 + n, 1);
  fill(b + 1, b + 1 + n, 1);
  for (int i = 0; i != m; ++i) {
    int x, y;
    cin >> x >> y;
    a[x] = 0;
    b[y] = 0;
  }
  int sum = 0;
  for (int i = 2; i <= n - 1; ++i) {
    int t = a[i] + a[n + 1 - i] + b[i] + b[n + 1 - i];
    if (i == n + 1 - i)
      sum += min(2, t);
    else
      sum += t;
  }
  cout << sum / 2 << endl;
}
