code: public static final int readNaturalNumber(OInput dis) throws IOException {
  
  		int naturalNumber = 0;
  		byte b1 = dis.readByte();
  		
  		if( b1 >= 0) {
  			naturalNumber = b1;
  		} else {
  			byte b2 = dis.readByte();
  			
  			if(b2 >= 0) {
  				naturalNumber = b1 * dv1 * -1 ;
  				naturalNumber += b2;
  			} else {
  				
  				byte b3 = dis.readByte();
  				
  				if(b3 >= 0) {
  					naturalNumber += b1  * dv2 * -1;
  					naturalNumber += (b2+1) * dv1 * -1;
  					naturalNumber += b3;
  				} else {
  					byte b4 = dis.readByte();
  					
  					if(b4 >=0) {
  						naturalNumber += b1  * dv3 * -1;
  						naturalNumber += (b2+1) * dv2 * -1;
  						naturalNumber += (b3+1) * dv1 * -1;
  						naturalNumber += b4;
  						
  					} else {
  						byte b5 = dis.readByte();
  
  						naturalNumber += b1  * dv4 * -1;
  						naturalNumber += (b2+1) * dv3 * -1;
  						naturalNumber += (b3+1) * dv2 * -1;
  						naturalNumber += (b4+1) * dv1 * -1;
  						naturalNumber += b5;
  
  					}
  				}
  			}
  		}
  		
  		return naturalNumber;
  	}
docs: DataInputStreamに対して、可変バイト数の自然数の読込みを実施する。
  @param dis
  @return 読み込んだ自然数
  @throws IOException