p, q, r, k = read_line.split.map(&.to_i64)
k -= 3
p, q, r = {p, q, r}.map { |x| x % 10 }
count = [nil.as(Int64?)] * 1000
array = [] of Int64
k.times do |now|
  x = p*100 + q*10 + r
  if cnt = count[x]
    cycle = now - cnt
    pos = (k - cnt) % cycle
    puts array[cnt + pos] % 10
    exit
  end
  count[x] = now
  array << x
  p, q, r = {q, r, p + q + r}.map { |x| x % 10 }
end
puts r