from itertools import combinations  
n=int(input())
s=input().split()
k=int(input())
l=len(list(combinations(s,k)))
counter=0
for i in list(combinations(s,k)):
        if 'a' in i:counter+=1 
print(counter/l)

from itertools import combinations listlen=int(input()) strs=list(map(str,input().split())) strlists=[] for i in strs: if i.isalpha(): strlists.append(i) indexcount=int(input()) index_tulpes=[] for i in range((listlen-indexcount+1)): index_tulpes.append(combinations(strlists,indexcount)) combos=[] for combo_iter in index_tulpes: for combo in combo_iter: combos.append(combo)

for i in combos:

print(i)

count=0 totalcombo_count=0 for i in combos: totalcombo_count+=1 if 'a' in i: count+=1

print(count)

print(totalcombo_count)

print(count/totalcombo_count)

dynamic for taking strings input

from itertools import combinations listlen=int(input()) strlists=[] for i in range(listlen): alphas=input() if alphas.isalpha(): strlists.append(alphas) indexcount=int(input()) index_tulpes=[] for i in range((listlen-indexcount+1)): index_tulpes.append(combinations(strlists,indexcount)) combos=[] for combo_iter in index_tulpes: for combo in combo_iter: combos.append(combo)

for i in combos:

print(i)

count=0 totalcombo_count=0 for i in combos: totalcombo_count+=1 if 'a' in i: count+=1

print(count)

print(totalcombo_count)

print(count/totalcombo_count)

from itertools import combinations n = int(input().strip()) S = input().strip().split() k = int(input().strip())

lst = list(combinations(sorted(S),k)) probabilities = list(filter(lambda x: 'a' in x,lst))

print(len(probabilities)/len(lst))

import itertools n= int(input()) letters= [i for i in input().split()] k= int(input()) c= list(itertools.combinations(letters, k)) possibilities= len([1 for i in c if 'a' in i ])/len(c) print(round(possibilities, 3))

![](# Enter your code here. Read input from STDIN. Print output to STDOUT

from itertools import combinations

n = int(input())

nums = input().split()

k = int(input())

lst = list(combinations(nums,k))

count = len(list(filter(lambda x: 'a' in x ,lst)))

print((count)/len(lst))https://)