# 1102.py

def cesare (a,k):
  o=ord('A')
  v=[chr(o+(ord(x)-o+k)%26) for x in a]
  return ''.join(v)

a='CRASCASTRAMOVEBO'

u=cesare(a,3); print (u)
# FUDVFDVWUDPRYHER

v=cesare(u,-3); print (v)
# CRASCASTRAMOVEBO