#include <bits/stdc++.h>
using namespace std;
const int MAXN = 1e3 + 10;
int main() {
  int n, m;
  while (~scanf("%d%d", &n, &m)) {
    int i, j;
    int x, y;
    bool row[MAXN], col[MAXN];
    memset(row, false, sizeof(row));
    memset(col, false, sizeof(col));
    for (i = 1; i <= m; i++) {
      scanf("%d%d", &x, &y);
      row[x] = true;
      col[y] = true;
    }
    int cnt = 0;
    for (i = 2; i <= n - 1; i++) {
      cnt += !row[i] + !col[i];
    }
    if (n % 2 && !row[n / 2 + 1] && !col[n / 2 + 1]) --cnt;
    printf("%d\n", cnt);
  }
  return 0;
}
