# digdig-q10
# Section 6, Q.10, p.24, p.249
# input: 123456

def digsum(n):
  m = n
  s = 0
  while m > 0:
    s += m%10
    m = m//10
  return s

n = int(input("n=? "))
while n >= 10:
  n = digsum(n)
  print(n)