#include <bits/stdc++.h>
using namespace std;
const int MAXN = 1000;
bool g[MAXN][MAXN];
bool mh[MAXN], mv[MAXN];
bool use[MAXN];
int main() {
  int n, m;
  cin >> n >> m;
  for (int i = 0; i < m; i++) {
    int a, b;
    cin >> a >> b;
    a--;
    b--;
    g[a][b] = true;
    mv[a] = true;
    mh[b] = true;
  }
  int ans = 0;
  for (int i = 1; i < n - 1; i++) ans += !mh[i] + !mv[i];
  if (n % 2 && !mh[n / 2] && !mv[n / 2]) ans--;
  cout << ans << endl;
  return 0;
}
