#include <bits/stdc++.h>
using namespace std;
const int INF = 1e9 + 23;
const int MOD = 1e9 + 7;
const int N = 1000 + 10;
int brow[N], bcol[N];
int main() {
  ios_base::sync_with_stdio(0);
  int n, m;
  cin >> n >> m;
  for (int i = 0; i < (m); ++i) {
    int x, y;
    cin >> x >> y;
    brow[x] = true;
    bcol[y] = true;
  }
  int ans = 0;
  for (int i = (2); i < (n); ++i) {
    if (i == n - i + 1)
      ans += !brow[i] || !bcol[i];
    else {
      ans += !brow[i];
      ans += !bcol[i];
    }
  }
  cout << ans << "\n";
  return 0;
}
