Buggy python submission (verdict: Runtime Error):
string = input()
k = int(input())
if len(string) > k:
    substrs = set()
    ls = sorted(list(string))
    for i in range(3):
        for s, c in enumerate(string):
            if c == ls[i]:
                for l in range(1, k+1):
                    substrs.add(string[s:s+l])
    substrs = list(substrs)
    substrs.sort()
    print(substrs[k-1])

else:
    substrs = set()
    for leng in range(1, len(string) + 1):
        for s in range(0, len(string) - leng + 1):
            substrs.add(string[s:s+leng])
    substrs = list(substrs)
    substrs.sort()
    print(substrs[k-1])


Fixed submission:
string = input()
k = int(input())
if len(string) > k:
    substrs = set()
    ls = sorted(list(string))
    for i in range(k):
        for s, c in enumerate(string):
            if c == ls[i]:
                for l in range(1, k+1):
                    substrs.add(string[s:s+l])
    substrs = list(substrs)
    substrs.sort()
    print(substrs[k-1])

else:
    substrs = set()
    for leng in range(1, len(string) + 1):
        for s in range(0, len(string) - leng + 1):
            substrs.add(string[s:s+leng])
    substrs = list(substrs)
    substrs.sort()
    print(substrs[k-1])

Buggy python submission (verdict: Runtime Error):
string = input()
k = int(input())
if len(string) >= k:
    substrs = set()
    ls = sorted(list(string))
    for i in range(k):
        for s, c in enumerate(string):
            if c == ls[i]:
                for l in range(1, k+1):
                    substrs.add(string[s:s+l])
    substrs = list(substrs)
    substrs.sort()
    print(substrs[k-1])

else:
    substrs = set()
    for leng in range(1, len(string)):
        for s in range(0, len(string) - leng):
            substrs.add(string[s:s+leng])
    substrs = list(substrs)
    substrs.sort()
    print(substrs[k-1])


Fixed submission:
string = input()
k = int(input())
if len(string) > k:
    substrs = set()
    ls = sorted(list(string))
    for i in range(k):
        for s, c in enumerate(string):
            if c == ls[i]:
                for l in range(1, k+1):
                    substrs.add(string[s:s+l])
    substrs = list(substrs)
    substrs.sort()
    print(substrs[k-1])

else:
    substrs = set()
    for leng in range(1, len(string) + 1):
        for s in range(0, len(string) - leng + 1):
            substrs.add(string[s:s+leng])
    substrs = list(substrs)
    substrs.sort()
    print(substrs[k-1])

Buggy python submission (verdict: Runtime Error):
string = input()
k = int(input())
if len(string) >= k:
    substrs = set()
    ls = sorted(list(string))
    for i in range(5):
        for s, c in enumerate(string):
            if c == ls[i]:
                for l in range(1, 5+1):
                    substrs.add(string[s:s+l])
    substrs = list(substrs)
    substrs.sort()
    print(substrs[k-1])

else:
    substrs = set()
    for leng in range(1, len(string)):
        for s in range(0, len(string) - leng):
            substrs.add(string[s:s+leng])
    substrs = list(substrs)
    substrs.sort()
    print(substrs[k-1])


Fixed submission:
string = input()
k = int(input())
if len(string) > k:
    substrs = set()
    ls = sorted(list(string))
    for i in range(k):
        for s, c in enumerate(string):
            if c == ls[i]:
                for l in range(1, k+1):
                    substrs.add(string[s:s+l])
    substrs = list(substrs)
    substrs.sort()
    print(substrs[k-1])

else:
    substrs = set()
    for leng in range(1, len(string) + 1):
        for s in range(0, len(string) - leng + 1):
            substrs.add(string[s:s+leng])
    substrs = list(substrs)
    substrs.sort()
    print(substrs[k-1])