Perfect Election
----------------
In a country (my memory fails to say which), the candidates {1, 2 ... N} 
are running in the parliamentary election.  An opinion poll asks the 
question "For any two candidates of your own choice, which election result 
would make you happy?".  The accepted answers are shown in the table below, 
where the candidates i and j are not necessarily different, i.e. it may 
happen that i=j.  There are M poll answers, some of which may be similar 
or identical.  The problem is to decide whether there can be an election 
outcome that conforms to all M answers.  We say that such an election outcome 
is perfect.  The result of the problem is 1 if a perfect election outcome 
does exist and 0 otherwise.

Input
-----
The input consists of multiple data sets.  Each data set corresponds to an 
instance of the problem and starts with two integral numbers: 1 <= N <= 1000 
and 1 <= M <= 1000000.  The data set continues with M pairs i j of signed 
numbers, 1 <= i,j <= N. Each pair encodes a poll answer as follows:

Accepted answers to the poll question                                        | Encoding
---------------------------------------------------------------------------------------
I would be happy if at least one from i and j is elected.                    | +i +j
I would be happy if at least one from i and j is not elected.                | -i -j
I would be happy if i is elected or j is not elected or both events happen.  | +i -j
I would be happy if i is not elected or j is elected or both events happen.  | -i +j

The input data are separated by white spaces and are correct.  The input is 
terminated by 0 0 (this data set should not be considered).

Output
------
For each data set the program prints the result of the encoded election problem. 
The result, 1 or 0, is printed on the standard output from the beginning of a line. 
There must be no empty lines on output.

Sample Input
------------
3 3 
+1 +2 
-1 +2 
-1 -3
2 3 
-1 +2 
-1 -2 
+1 -2
2 4 
-1 +2 
-1 -2 
+1 -2 
+1 +2
2 8 
+1 +2 
+2 +1 
+1 -2 
+1 -2 
-2 +1 
-1 +1 
-2 -2 
+1 -1
0 0

Sample Output
-------------
1
1
0
1