question: How many months passed between the Ottoman force defeated 4,000 Serbs at Demotika and the first unsuccessful attempt to seize Constantinople was made by John V?
#1 return the  Ottoman force defeated 4,000 Serbs at Demotika 
#2 return the  first unsuccessful attempt to seize Constantinople made by John V 
#3 return month of #1 
#4 return month of #2 
#5 return the  difference of #4 and  #3