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  1. Prepare
  2. Python
  3. Itertools
  4. Iterables and Iterators
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Iterables and Iterators

  • GEvil
     + 0 comments
    # Enter your code here. Read input from STDIN. Print output to STDOUT
from itertools import combinations
N=int(input())
li=list(map(str,input().split(" ")))
K=int(input())

comb=list(combinations(li,K))

c=0
for i in comb:
    if 'a' in i:
        c+=1
print(float(c/len(comb)))