#include <bits/stdc++.h>
using namespace std;
const int MAX_N = 1100;
const int INF = 1 << 28;
const double EPS = 1e-9;
const double PI = 3.14159265358979;
int n, m;
bool banned[MAX_N][MAX_N];
int main() {
  cin >> n >> m;
  memset(banned, false, sizeof(banned));
  for (int i = (0); i < (m); i++) {
    int y, x;
    cin >> x >> y;
    y--, x--;
    banned[y][x] = true;
  }
  int r = 0;
  bool center = false;
  for (int i = (0); i < (n); i++) {
    if (i == 0 || i == n - 1) continue;
    bool ok = true;
    for (int j = (0); j < (n); j++) {
      if (banned[i][j]) {
        ok = false;
        break;
      }
    }
    if (n % 2 == 1 && i == n / 2) center = ok;
    r += ok;
  }
  for (int j = (0); j < (n); j++) {
    if (j == 0 || j == n - 1 || (center && j == n / 2)) continue;
    bool ok = true;
    for (int i = (0); i < (n); i++) {
      if (banned[i][j]) {
        ok = false;
        break;
      }
    }
    r += ok;
  }
  cout << r << endl;
  return 0;
}
