#include <bits/stdc++.h>
using namespace std;
bool w[1005];
bool h[1005];
int main() {
  int n, m;
  scanf("%d %d", &n, &m);
  for (int i = 0; i < n; i++) w[i] = h[i] = true;
  for (int i = 0; i < m; i++) {
    int x, y;
    scanf("%d %d", &x, &y);
    x--;
    y--;
    w[x] = false;
    h[y] = false;
  }
  int ret = 0;
  for (int i = 1; i < n - 1; i++) {
    int s = i, e = n - i - 1;
    if (s == e) {
      if (w[s] || h[s]) ret++;
    } else {
      int cnt = w[s] + w[e] + h[s] + h[e];
      ret += cnt;
    }
    w[s] = w[e] = h[s] = h[e] = false;
  }
  printf("%d\n", ret);
  return 0;
}
