#include <bits/stdc++.h>
std::mt19937 rng(
    (int)std::chrono::steady_clock::now().time_since_epoch().count());
template <class T = int>
class Dinic {
 public:
  struct Edge {
    Edge(int a, T b) {
      to = a;
      cap = b;
    }
    int to;
    T cap;
  };
  Dinic(int _n) {
    this->n = _n;
    edges.resize(n);
  }
  T maxFlow(int src, int sink) {
    T ans = 0;
    while (bfs(src, sink)) {
      T flow;
      pt = std::vector<int>(n, 0);
      while (flow = dfs(src, sink)) {
        ans += flow;
      }
    }
    return ans;
  }
  void addEdge(int from, int to, T cap = 1) {
    edges[from].push_back(list.size());
    list.push_back(Edge(to, cap));
    edges[to].push_back(list.size());
    list.push_back(Edge(from, 0));
  }

 private:
  int n;
  std::vector<std::vector<int> > edges;
  std::vector<Edge> list;
  std::vector<int> h, pt;
  T dfs(int on, int sink, T flow = 1e9) {
    if (flow == 0) {
      return 0;
    }
    if (on == sink) {
      return flow;
    }
    for (; pt[on] < edges[on].size(); pt[on]++) {
      int cur = edges[on][pt[on]];
      if (h[on] + 1 != h[list[cur].to]) {
        continue;
      }
      T got = dfs(list[cur].to, sink, std::min(flow, list[cur].cap));
      if (got) {
        list[cur].cap -= got;
        list[cur ^ 1].cap += got;
        return got;
      }
    }
    return 0;
  }
  bool bfs(int src, int sink) {
    h = std::vector<int>(n, n);
    h[src] = 0;
    std::queue<int> q;
    q.push(src);
    while (!q.empty()) {
      int on = q.front();
      q.pop();
      for (auto a : edges[on]) {
        if (list[a].cap == 0) {
          continue;
        }
        int to = list[a].to;
        if (h[to] > h[on] + 1) {
          h[to] = h[on] + 1;
          q.push(to);
        }
      }
    }
    return h[sink] < n;
  }
};
int main() {
  std::ios_base::sync_with_stdio(false);
  std::cin.tie(NULL);
  int n, m;
  std::cin >> n >> m;
  std::vector<bool> rows(n, false), cols(n, false);
  rows[0] = rows[n - 1] = cols[0] = cols[n - 1] = true;
  while (m--) {
    int x, y;
    std::cin >> x >> y;
    x--;
    y--;
    rows[x] = cols[y] = true;
  }
  int ans = 0;
  for (int i = 1; i + 1 < n; i++) {
    if (n % 2 == 1 && i == n / 2) {
      continue;
    }
    if (!rows[i]) {
      ans++;
    }
    if (!cols[i]) {
      ans++;
    }
  }
  if (n % 2 == 1 && (!rows[n / 2] || !cols[n / 2])) {
    ans++;
  }
  std::cout << ans << '\n';
}
