#include <bits/stdc++.h>
using namespace std;
const int MAX = 1000;
bool col[MAX];
bool row[MAX];
int main(int argc, char* argv[]) {
  int n;
  cin >> n;
  int m;
  cin >> m;
  col[0] = col[n - 1] = row[0] = row[n - 1] = true;
  for (int i = 0; i < m; ++i) {
    int x, y;
    cin >> x >> y;
    col[x - 1] = row[y - 1] = true;
  }
  int ans = 0;
  for (int i = 0; i < n; ++i) {
    if (!col[i]) ++ans;
    if (!row[i]) ++ans;
  }
  if ((n & 1) && !col[n / 2] && !row[n / 2]) --ans;
  cout << ans;
  return 0;
}
