#include <bits/stdc++.h>
using namespace std;
int n, m, r, c, R[1005], C[1005];
int main() {
  cin.tie(0);
  cin.sync_with_stdio(0);
  cin >> n >> m;
  R[1] = C[1] = R[n] = C[n] = 1;
  for (int i = 1; i <= m; i++) {
    cin >> r >> c;
    R[r] = 1;
    C[c] = 1;
  }
  int ans = 0;
  for (int i = 1; i <= n; i++) {
    if (!C[i]) ans++;
    if (!R[i]) ans++;
  }
  if (n % 2 && !C[n / 2 + 1] && !R[n / 2 + 1]) ans--;
  printf("%d\n", ans);
  return 0;
}
