#include <bits/stdc++.h>
using namespace std;
bool fr[1010], fc[1010];
int n, m;
int main() {
  cin >> n >> m;
  for (int i = 0; i < m; ++i) {
    int a, b;
    cin >> a >> b;
    fr[a] = true;
    fc[b] = true;
  }
  fr[1] = fr[n] = fc[1] = fc[n] = true;
  int cnt = 0;
  for (int i = 1; i <= n; ++i) {
    if (n == i * 2 - 1) {
      if (!fr[i] || !fc[i]) ++cnt;
      continue;
    }
    if (!fr[i]) ++cnt;
    if (!fc[i]) ++cnt;
  }
  cout << cnt << endl;
}
