#include <bits/stdc++.h>
using namespace std;
const int N = 1000;
int n, m, row[N], col[N];
inline int calc(int c) {
  return col[c] + col[n - c - 1] + row[c] + row[n - c - 1];
}
int main() {
  scanf("%d%d", &n, &m);
  for (int i = 0; i < n; ++i) row[i] = col[i] = 1;
  for (int i = 0; i < m; ++i) {
    int x, y;
    scanf("%d%d", &x, &y);
    --x, --y;
    row[x] = col[y] = 0;
  }
  int res = 0, mid = n >> 1;
  if ((n & 1) == 1 && (row[mid] == 1 || col[mid] == 1)) ++res;
  for (int i = 1; i < mid; ++i)
    res += col[i] + col[n - i - 1] + row[i] + row[n - i - 1];
  printf("%d\n", res);
  return 0;
}
