#include <bits/stdc++.h>
const int M = 1005;
using namespace std;
inline int read() {
  char c = getchar();
  int x = 0, w = 1;
  while (c > '9' || c < '0') {
    if (c == '-') w = -1;
    c = getchar();
  }
  while (c >= '0' && c <= '9') {
    x = x * 10 + c - '0';
    c = getchar();
  }
  return x * w;
}
int n, m, Ans;
bool hvis[M], lvis[M];
int main() {
  n = read();
  m = read();
  for (int i = 1, x, y; i <= m; i++) {
    x = read(), y = read();
    hvis[x] = lvis[y] = true;
  }
  for (int i = 2; i < n; i++) Ans += (hvis[i] ^ 1) + (lvis[i] ^ 1);
  if (n % 2 && !hvis[n / 2 + 1] && !lvis[n / 2 + 1]) --Ans;
  cout << Ans << endl;
  return 0;
}
