func_code_string: #include <bits/stdc++.h>   using namespace std;   int n, m, i, x, y, ans = 0, t;   bool p1[1010], p2[1010];   int main() {     scanf( %d%d , &n, &m);     for (i = 1; i <= n; i++) p1[i] = p2[i] = 1;     p1[1] = p2[1] = p1[n] = p2[n] = 0;     for (i = 1; i <= m; i++) {       scanf( %d%d , &x, &y);       p1[x] = p2[y] = 0;     }     ans = 2 * (n - 2);     for (i = 2; i < n; i++) {       if (p1[i] == 0) ans--;       if (p2[i] == 0) ans--;     }     if (n % 2) {       t = n / 2 + 1;       if (p1[t] == 0) ans++;       if (p2[t] == 0) ans++;       ans -= 2;       if (p1[t] || p2[t]) ans++;     }     cout << ans << endl;     return 0;   }   