#include <bits/stdc++.h>
using namespace std;
bool banr[1005], banc[1005];
int n, m, a, b, ans;
int main(int argc, char **argv) {
  while (~scanf("%d%d", &n, &m)) {
    memset(banr, 0, sizeof(banr));
    memset(banc, 0, sizeof(banc));
    ans = 0;
    while (m--) {
      scanf("%d%d", &a, &b);
      banr[a] = banc[b] = 1;
    }
    for (int i = 2; i < n; ++i)
      if (i != n - i + 1)
        ans += !banr[i] + !banc[i];
      else
        ans += (!banr[i] || !banc[i]);
    printf("%d\n", ans);
  }
  return 0;
}
