Task: Question Answering
Input (English): Problem: a total of 520 players participated in a single tennis knock out tournament . what is the total number of matches played in the tournament ? ( knockout means if a player loses , he is out of the tournament ) . no match ends in a tie . 
Options: a ) 511 , b ) 519 , c ) 256 , d ) 255 , e ) 1023
Output (English): b