a=gets.split(" ").map{|e| e.to_i}.sort
if a[0]==a[2] then
	puts a[0]
elsif  a.uniq.size==2 then
	puts (a[0]==a[1])?a[2]:(a[0])
else
	puts [0,1,2,3].select{|e| a.count{|e2| e2==e}==0}
end