#include <bits/stdc++.h>
using namespace std;
const int MxN = 50;
vector<vector<int> > arr_;
int main() {
  ios_base::sync_with_stdio(false);
  int n, m;
  cin >> n >> m;
  set<int> row, col;
  row.insert(1);
  row.insert(n);
  col.insert(1);
  col.insert(n);
  for (int i = 0; i < m; i++) {
    int a, b;
    cin >> a >> b;
    row.insert(a);
    col.insert(b);
  }
  int mini = min(row.size(), col.size());
  int ans = 0;
  for (int i = 1; i <= n; i++) {
    bool r = 0;
    if (row.find(i) == row.end()) {
      ans++;
      r = 1;
    }
    if (col.find(i) == col.end()) {
      if (!r || i * 2 - 1 != n) ans++;
    }
  }
  cout << ans << endl;
  return 0;
}
