Buggy python submission (verdict: Time Limit Exceeded):
import sys
read = sys.stdin.read
readlines = sys.stdin.readlines
from collections import defaultdict
def main():
    s = list(input())
    k = int(input())
    k -= 1

    d1 = defaultdict(list)
    for i, c in enumerate(s):
        d1[c].append(i)
    d2 = sorted(d1.items())

    lens = len(s)
    for d2e in d2:
        subs = set()
        subs.add(d2e[0])
        for d2ee in d2e[1]:
            for i1 in range(d2ee+1, lens + 1):
                subs.add("".join(s[d2ee:i1]))
        if len(subs) > k:
            subsl = list(subs)
            subsl.sort()
            print(subsl[k])
            sys.exit()
        else:
            k -= len(subs)


if __name__ == '__main__':
    main()

Fixed submission:
import sys
read = sys.stdin.read
readlines = sys.stdin.readlines
from collections import defaultdict
def main():
    s = list(input())
    k = int(input())
    k -= 1

    d1 = defaultdict(list)
    for i, c in enumerate(s):
        d1[c].append(i)
    d2 = sorted(d1.items())

    lens = len(s)
    for d2e in d2:
        subs = set()
        subs.add(d2e[0])
        for d2ee in d2e[1]:
            end = min(lens + 1, d2ee + k + 2)
            for i1 in range(d2ee+1, end):
                subs.add("".join(s[d2ee:i1]))
        if len(subs) > k:
            subsl = list(subs)
            subsl.sort()
            print(subsl[k])
            sys.exit()
        else:
            k -= len(subs)

if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
import sys
read = sys.stdin.read
readlines = sys.stdin.readlines
def main():
    s = list(input())
    k = int(input())
    subs = set()
    lens = len(s)
    for i1 in range(lens):
        for i2 in range(lens - i1):
            subs.add("".join(s[i2:i2+i1+1]))
    subs_l = list(subs)
    subs_l.sort()
    print(subs_l[k-1])


if __name__ == '__main__':
    main()

Fixed submission:
import sys
read = sys.stdin.read
readlines = sys.stdin.readlines
from collections import defaultdict
def main():
    s = list(input())
    k = int(input())
    k -= 1

    d1 = defaultdict(list)
    for i, c in enumerate(s):
        d1[c].append(i)
    d2 = sorted(d1.items())

    lens = len(s)
    for d2e in d2:
        subs = set()
        subs.add(d2e[0])
        for d2ee in d2e[1]:
            end = min(lens + 1, d2ee + k + 2)
            for i1 in range(d2ee+1, end):
                subs.add("".join(s[d2ee:i1]))
        if len(subs) > k:
            subsl = list(subs)
            subsl.sort()
            print(subsl[k])
            sys.exit()
        else:
            k -= len(subs)

if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
import sys
read = sys.stdin.read
readlines = sys.stdin.readlines
def main():
    s = list(input())
    k = int(input())
    subs = set()
    lens = len(s)
    for i1 in range(lens):
        for i2 in range(lens - i1):
            subs.add("".join(s[i2:i2+i1+1]))
    subs_l = list(subs)
    subs_l.sort()
    print(subs_l[k-1])


if __name__ == '__main__':
    main()

Fixed submission:
import sys
read = sys.stdin.read
readlines = sys.stdin.readlines
from collections import defaultdict
def main():
    s = list(input())
    k = int(input())
    k -= 1

    d1 = defaultdict(list)
    for i, c in enumerate(s):
        d1[c].append(i)
    d2 = sorted(d1.items())

    lens = len(s)
    for d2e in d2:
        subs = set()
        subs.add(d2e[0])
        for d2ee in d2e[1]:
            end = min(lens + 1, d2ee + k + 2)
            for i1 in range(d2ee+1, end):
                subs.add("".join(s[d2ee:i1]))
        if len(subs) > k:
            subsl = list(subs)
            subsl.sort()
            print(subsl[k])
            sys.exit()
        else:
            k -= len(subs)

if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
def main():
    s = list(input())
    k = int(input())
    lens = len(s)
    subs = []
    for i1 in range(1, lens + 1):
        for i2 in range(0, lens +1 - i1):
            subs.append(tuple(s[i2:i1+i2]))
    subs = set(subs)
    subs = list(subs)
    subs.sort()
    r = subs[k-1]
    print("".join(r))

if __name__ == '__main__':
    main()

Fixed submission:
import sys
read = sys.stdin.read
readlines = sys.stdin.readlines
from collections import defaultdict
def main():
    s = list(input())
    k = int(input())
    k -= 1

    d1 = defaultdict(list)
    for i, c in enumerate(s):
        d1[c].append(i)
    d2 = sorted(d1.items())

    lens = len(s)
    for d2e in d2:
        subs = set()
        subs.add(d2e[0])
        for d2ee in d2e[1]:
            end = min(lens + 1, d2ee + k + 2)
            for i1 in range(d2ee+1, end):
                subs.add("".join(s[d2ee:i1]))
        if len(subs) > k:
            subsl = list(subs)
            subsl.sort()
            print(subsl[k])
            sys.exit()
        else:
            k -= len(subs)

if __name__ == '__main__':
    main()