void BFS(int x, int y)
{
    int ii, jj, i, j;
    while(!Q.empty())
    {
        i = Q.front().first;
        j = Q.front().second;
        Q.pop();
        for(int l = 0 ; l < 8 ; ++l)
        {
            ii = i + dx[l];
            jj = j + dy[l];
            if(Interior(ii, jj) && A[ii][jj] == 0 )
            {
                Q.push(make_pair(ii, jj));
                A[ii][jj] = 1 + A[i][j];
            }
        }
    }
}