question: How many volunteers were from Sofia, Tirnovo, and Pazardzhik combined?
#1 return volunteers 
#2 return #1 from  Sofia 
#3 return #1 from  Tirnovo 
#4 return #1 from  Pazardzhik 
#5 return number of  #2 
#6 return number of  #3 
#7 return number of  #4 
#8 return sum of #5 and  #6 
#9 return sum of #7 and  #8