#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 50, mod = 1000000007;
int modd(int a, int m) { return ((a % m) + m) % m; }
void min_self(int& a, int b) { a = min(a, b); }
void max_self(int& a, int b) { a = max(a, b); }
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int n, m;
  cin >> n >> m;
  bool row[n], col[n];
  memset(row, 0, sizeof row);
  memset(col, 0, sizeof col);
  int x, y;
  for (int i = 0; i < m; ++i) {
    cin >> x >> y;
    --x;
    --y;
    row[y] = true;
    col[x] = true;
  }
  int ans = 0;
  for (int i = 1; i < n - 1; ++i) {
    if (!row[i] && !col[i]) {
      if (n % 2 == 1 && i == n / 2)
        ++ans;
      else
        ans += 2;
    } else if (!row[i] || !col[i])
      ++ans;
  }
  cout << ans;
  return 0;
}
