private String read_block(char[][] ct)
	{
		//read the block horizontally 
		StringBuilder sb=new StringBuilder();
		for(int i=0;i<ct[0].length;i+=period)
		{
			int end=i+period>ct[0].length?ct[0].length:i+period;
			for(int j=0;j<ct.length;j++)
			{
				for(int k=i;k<end;k++)
				{
					if(ct[j][k]!='\0')
					{
					 sb.append(ct[j][k]);
					}
				}
			}
		}
		return sb.toString();
	}