#include <bits/stdc++.h>
using namespace std;
int n, m, i, j, t1, t2, flag, x, y, tot;
int f[1005][1005], g1[1005], g2[1005];
int main() {
  while (~scanf("%d%d", &n, &m)) {
    for (i = 1; i <= n; i++)
      for (j = 1; j <= n; j++) f[i][j] = 0;
    for (i = 1; i <= n; i++) g1[i] = g2[i] = 0;
    for (i = 1; i <= m; i++) {
      scanf("%d%d", &x, &y);
      f[x][y] = 1;
    }
    for (i = 2; i <= n - 1; i++) {
      flag = 1;
      for (j = 1; j <= n; j++)
        if (f[i][j] != 0) {
          flag = 0;
          break;
        }
      if (flag) g1[i] = 1;
    }
    for (i = 2; i <= n - 1; i++) {
      flag = 1;
      for (j = 1; j <= n; j++)
        if (f[j][i] != 0) {
          flag = 0;
          break;
        }
      if (flag) g2[i] = 1;
    }
    tot = 0;
    for (i = 1; i <= n; i++) {
      if (g1[i]) tot++;
      if (g2[i]) tot++;
    }
    if (n % 2 == 1 && g1[n / 2 + 1] == 1 && g2[n / 2 + 1] == 1) tot--;
    printf("%d\n", tot);
  }
}
