public String read_block(char[][] block)
	{
		int col=block[0].length;
		StringBuilder sb=new StringBuilder();
		int start_row=0;
		int total_row=block.length;
		while(start_row<total_row)
		{
			int end_row=start_row+5>=total_row?total_row:start_row+5;
			//int read=remain_row<5?remain_row:5;
			for(int i=0;i<col;i++)
			{
			  for(int j=start_row;j<end_row;j++)
			  {
				  if(block[j][i]!='\0')
				  {
				    sb.append(block[j][i]);
				  }
			  }
			}
			start_row=end_row;
		}
		return sb.toString();
	}