from fractions import Fraction 
from itertools import combinations

bag_1=['r','r','r','r','b','b','b','b','b']
bag_2=['r','r','r','b','b','b','b','b','b','b']
all_pairs=[]
num=0
for item1_bag_1 in (bag_1):
  for item2_bag_2,item3_bag2 in (combinations(bag_2,2)):
    all_pairs.append((item1_bag_1,item2_bag_2,item3_bag2))
for bbr in all_pairs:
  if bbr.count('r')==1 and bbr.count('b')==2:
    num+=1
print(Fraction(num,len(all_pairs)))