Buggy python submission (verdict: Time Limit Exceeded):
s = input()
x = int(input())
n = len(s)

pos = [[] for __ in range(256)]
for i in range(n):
    pos[ord(s[i])].append(i)

f = {}
for c in range(97, 123):
    for i in pos[c]:
        for j in range(i, n):
            f[s[i:j+1]] = 1
    if len(f) >= x:
        break

def cmp(u, v):
    while len(u) < len(v): u = u + '1'
    while len(u) > len(v): v = v + '1'
    return u > v

p = [u for u in f]
for i in range(len(p)):
    for j in range(i+1, len(p)):
        if cmp(p[i], p[j]):
            p[i], p[j] = p[j], p[i]

print(p[x - 1])

Fixed submission:
s = input()
x = int(input())
n = len(s)

pos = [[] for __ in range(256)]
for i in range(n):
    pos[ord(s[i])].append(i)

f = set()
for c in range(97, 123):
    for i in pos[c]:
        for j in range(x):
            f.add(s[i:i+j+1])
    if len(f) >= x:
        break

p = [u for u in f]
p.sort()
print(p[x - 1])

Buggy python submission (verdict: Time Limit Exceeded):
s = input()
x = int(input())
n = len(s)

pos = [[] for __ in range(256)]
for i in range(n):
    pos[ord(s[i])].append(i)

f = set()
for c in range(97, 123):
    for i in pos[c]:
        for j in range(i, n):
            f.add(s[i:j+1])
            if len(f) >= 1000:
                break
    if len(f) >= x:
        break

def cmp(u, v):
    while len(u) < len(v): u = u + '1'
    while len(u) > len(v): v = v + '1'
    return u > v

p = [u for u in f]
for i in range(len(p)):
    for j in range(i+1, len(p)):
        if cmp(p[i], p[j]):
            p[i], p[j] = p[j], p[i]

print(p[x - 1])

Fixed submission:
s = input()
x = int(input())
n = len(s)

pos = [[] for __ in range(256)]
for i in range(n):
    pos[ord(s[i])].append(i)

f = set()
for c in range(97, 123):
    for i in pos[c]:
        for j in range(x):
            f.add(s[i:i+j+1])
    if len(f) >= x:
        break

p = [u for u in f]
p.sort()
print(p[x - 1])

Buggy python submission (verdict: Time Limit Exceeded):
s = input()
x = int(input())
n = len(s)

pos = [[] for __ in range(256)]
for i in range(n):
    pos[ord(s[i])].append(i)

f = set()
for c in range(97, 123):
    for i in pos[c]:
        for j in range(i, n):
            f.add(s[i:j+1])
            if len(f) >= 10000:
                break
    if len(f) >= x:
        break

def cmp(u, v):
    while len(u) < len(v): u = u + '1'
    while len(u) > len(v): v = v + '1'
    return u > v

p = [u for u in f]
for i in range(len(p)):
    for j in range(i+1, len(p)):
        if cmp(p[i], p[j]):
            p[i], p[j] = p[j], p[i]

print(p[x - 1])

Fixed submission:
s = input()
x = int(input())
n = len(s)

pos = [[] for __ in range(256)]
for i in range(n):
    pos[ord(s[i])].append(i)

f = set()
for c in range(97, 123):
    for i in pos[c]:
        for j in range(x):
            f.add(s[i:i+j+1])
    if len(f) >= x:
        break

p = [u for u in f]
p.sort()
print(p[x - 1])

Buggy python submission (verdict: Time Limit Exceeded):
s = input()
x = int(input())
n = len(s)

pos = [[] for __ in range(256)]
for i in range(n):
    pos[ord(s[i])].append(i)

f = set()
for c in range(97, 123):
    for i in pos[c]:
        for j in range(i, n):
            f.add(s[i:j+1])
    if len(f) >= x:
        break

def cmp(u, v):
    while len(u) < len(v): u = u + '1'
    while len(u) > len(v): v = v + '1'
    return u > v

p = [u for u in f]
for i in range(len(p)):
    for j in range(i+1, len(p)):
        if cmp(p[i], p[j]):
            p[i], p[j] = p[j], p[i]

print(p[x - 1])

Fixed submission:
s = input()
x = int(input())
n = len(s)

pos = [[] for __ in range(256)]
for i in range(n):
    pos[ord(s[i])].append(i)

f = set()
for c in range(97, 123):
    for i in pos[c]:
        for j in range(x):
            f.add(s[i:i+j+1])
    if len(f) >= x:
        break

p = [u for u in f]
p.sort()
print(p[x - 1])