#include <bits/stdc++.h>
using namespace std;
bool graph[1010][1010], row[1010], col[1010];
int main(void) {
  int n, m;
  scanf("%d%d", &n, &m);
  if (n == 2) {
    puts("0");
    return 0;
  }
  memset(graph, false, sizeof(graph));
  memset(row, false, sizeof(row));
  memset(col, false, sizeof(col));
  for (int i = 0; i < m; ++i) {
    int x, y;
    scanf("%d%d", &x, &y);
    row[x] = true;
    col[y] = true;
  }
  int count = 0;
  if (n & 1) {
    if (!row[n / 2 + 1] || !col[n / 2 + 1]) {
      graph[n / 2 + 1][1] = true;
      row[n / 2 + 1] = true;
      graph[1][n / 2 + 1] = true;
      col[n / 2 + 1] = true;
      ++count;
    }
  }
  for (int i = 2; i <= n / 2; ++i) {
    if (!row[i]) {
      graph[i][1] = true;
      row[i] = true;
      ++count;
    }
  }
  for (int i = n / 2 + 1; i < n; ++i) {
    if (!row[i]) {
      graph[i][n] = true;
      row[i] = true;
      ++count;
    }
  }
  for (int i = 2; i <= n / 2; ++i) {
    if (!col[i]) {
      graph[n][i] = true;
      col[i] = true;
      ++count;
    }
  }
  for (int i = n / 2 + 1; i < n; ++i) {
    if (!col[i]) {
      graph[1][i] = true;
      col[i] = true;
      ++count;
    }
  }
  printf("%d\n", count);
  return 0;
}
