question: How many months after Marienburg, Dirschau and Eylau were taken was Kneiphof also taken?
#1 return Marienburg ,  Dirschau and  Eylau were taken 
#2 return Kneiphof was  taken 
#3 return when  was  #1 
#4 return when  was  #2 
#5 return difference of #4 and  #3 in  months