PROBLEM STATEMENT
When the Christmas dinner is over, it's time to sing carols.  Unfortunately, not all the family 
members know the lyrics to the same carols.  Everybody knows at least one, though.

You are given a vector <string> lyrics.  The j-th character of the i-th element of lyrics is 'Y' 
if the i-th person knows the j-th carol, and 'N' if he doesn't.  Return the minimal number of 
carols that must be sung to allow everyone to sing at least once.


DEFINITION
Class:CarolsSinging
Method:choose
Parameters:vector <string>
Returns:int
Method signature:int choose(vector <string> lyrics)


CONSTRAINTS
-lyrics will contain between 1 and 30 elements, inclusive.
-Each element of lyrics will contain between 1 and 10 characters, inclusive.
-Each element of lyrics will contain the same number of characters.
-Each element of lyrics will contain only 'Y' and 'N' characters.
-Each element of lyrics will contain at least one 'Y' character.


EXAMPLES

0)
{"YN","NY"}

Returns: 2

Both carols need to be sung.

1)
{"YN","YY","YN"}

Returns: 1

Everybody knows the first carol, so singing just that one is enough.

2)
{"YNN","YNY","YNY","NYY","NYY","NYN"}

Returns: 2

Singing the best known carol is not always the optimal strategy. Here, the optimal way is to pick 
the first two carols even though four people know the third one.

3)
{"YNNYYY","YYNYYY","YNNYYN","NYYNNN","YYYNNN","YYYNNY","NYYYYY","NYNYYY","NNNNYY",
 "YYYYYY","YNNNNN","YYYYNY","YYNNNN","NNYYYN","NNNNYY","YYYNNN","NYNNYN","YNNYYN",
 "YYNNNY","NYYNNY","NNYYYN","YNYYYN","NNNYNY","YYYYNN","YYNYNN","NYYNYY","YYNYYN"}

Returns: 4



 This problem statement is the exclusive and proprietary property of TopCoder, Inc. Any 
 unauthorized use or reproduction of this information without the prior written consent of 
 TopCoder, Inc. is strictly prohibited. (c)2010, TopCoder, Inc. All rights reserved.
 
  This problem statement is the exclusive and proprietary property of TopCoder, Inc. Any unauthorized use or reproduction of this information without the prior written consent of TopCoder, Inc. is strictly prohibited. (c)2010, TopCoder, Inc. All rights reserved.