#include <bits/stdc++.h>
using namespace std;
bitset<1010> R, C;
int n, m;
bool board[1010][1010];
int x, y;
int main() {
  scanf("%d %d", &n, &m);
  for (int i = 0; i < int(m); i++) {
    scanf("%d %d", &x, &y);
    board[x][y] = true;
  }
  for (int i = 2; i < n; i++) {
    R[i] = true;
    for (int j = 1; j <= n; j++)
      if (board[i][j]) R[i] = false;
    C[i] = true;
    for (int j = 1; j <= n; j++)
      if (board[j][i]) C[i] = false;
  }
  int cnt = 0;
  for (int i = 1; i <= n; i++) {
    if (R[i]) cnt++;
    if (C[i]) cnt++;
  }
  if (n % 2 == 1 && R[(n + 1) / 2] && C[(n + 1) / 2]) cnt--;
  printf("%d\n", cnt);
}
