require 'set'
a, b, c, k = gets.split.map(&:to_i)
a %= 10
b %= 10
c %= 10
k -= 1

list = []
seen = Set.new

while true do
  key = a * 100 + b * 10 + c
  if seen.include?(key)
    # found
    break
  end
  list << key
  seen << key
  x = (a + b + c) % 10
  a = b
  b = c
  c = x
end
k = (k - 2) % list.length
puts list[k] % 10