#include <bits/stdc++.h>
using namespace std;
bool row[1005], col[1005];
bool tb[1005][1005];
int main() {
  int n, m;
  cin >> n >> m;
  for (int i = 0; i < m; i++) {
    int a, b;
    cin >> a >> b;
    a--, b--;
    tb[a][b] = true;
  }
  for (int j = 0; j < n; j++) row[j] = col[j] = true;
  row[0] = row[n - 1] = col[0] = col[n - 1] = false;
  for (int i = 1; i < n - 1; i++)
    for (int j = 0; j < n; j++) {
      if (tb[i][j]) row[i] = false;
      if (tb[j][i]) col[i] = false;
    }
  int ans = 0;
  for (int i = 0; i < n / 2; i++) {
    int cnt = row[i] + col[i] + row[n - 1 - i] + col[n - 1 - i];
    ans += cnt;
  }
  if (n % 2) {
    if (row[n / 2])
      ans++;
    else if (col[n / 2])
      ans++;
  }
  cout << ans << endl;
  return 0;
}
