#include <bits/stdc++.h>
using namespace std;
int H[1000 + 5], L[1000 + 5];
int main() {
  int n, m;
  while (cin >> n >> m) {
    int ans = 0;
    memset(H, 0, sizeof(H));
    memset(L, 0, sizeof(L));
    int x, y;
    for (int i = 1; i <= m; i++) {
      cin >> x >> y;
      H[x] = 1;
      L[y] = 1;
    }
    for (int i = 2; i < n; i++) {
      if (H[i] + L[i] == 1)
        ans++;
      else if (H[i] + L[i] == 0) {
        if (n % 2 != 0 && (n + 1) / 2 == i)
          ans++;
        else
          ans = ans + 2;
      }
    }
    cout << ans << endl;
  }
  return 0;
}
