func_code_string: #include <bits/stdc++.h>   using namespace std;   const int MAXN = 1024;   int n, m;   bool b[MAXN][MAXN];   int main() {     cin >> n >> m;     for (register int l = (1); l < (int)(m + 1); ++l) {       int x, y;       cin >> x >> y;       x--;       y--;       b[x][y] = true;       for (register int xx = (x - 2); xx < (int)(x + 1); ++xx)         for (register int yy = (y - 2); yy < (int)(y + 1); ++yy)           if (xx >= 0 && yy >= 0) {             bool ok = true;             for (register int i = (0); i < (int)(3); ++i)               for (register int j = (0); j < (int)(3); ++j)                 if (!b[i + xx][j + yy]) ok = false;             if (ok) {               cout << l << endl;               return 0;             }           }     }     cout << -1 << endl;     return 0;   }   