import re

s = "aaaaaaaaabbbbbbbbccccccdddddaaaaaaaaaaaaaaaaaaaaaaa"
def encr(a):
  tabl = []
  while a != "":
    tabl.append(re.compile(r"^(.)\1{1,}").match(a).group())
    a = re.sub(r"^(.)\1{1,}", r"", a)
  return ''.join( [str(len(x))+x[0] for x in tabl] )

print(encr(s))