You are given a string s. Among the **different** substrings of s, print the K-th lexicographically smallest one.  A substring of s is a string obtained by taking out a non-empty contiguous part in s. For example, if s = `ababc`, `a`, `bab` and `ababc` are substrings of s, while `ac`, `z` and an empty string are not. Also, we say that substrings are different when they are different as strings.  Let X = x_{1}x_{2}...x_{n} and Y = y_{1}y_{2}...y_{m} be two distinct strings. X is lexicographically larger than Y if and only if Y is a prefix of X or x_{j} > y_{j} where j is the smallest integer such that x_{j} \neq y_{j}.
s = input()
k = int(input())
n = len(s)

substring = []

for i in range(min(n, k)):
    for j in range(n-i):
        substring.append(s[j:j+i+1])
        print(s[j:j+i+1], j, j+i+1)

substring = list(set(substring))
substring.sort()
print(substring)
#substring.pop(0)

print(substring[k-1])


s = input()
k = int(input())
n = len(s)

substring = []

for i in range(min(n, k)):
    for j in range(n-i):
        substring.append(s[j:j+i+1])
        

substring = list(set(substring))
substring.sort()
#print(substring)

print(substring[k-1])
