Buggy python submission (verdict: Runtime Error):
import sys
n = int(input())
length = int(n / 19) + 1
d = []
for i in range(length):
    d += list(map(int, input().split()))
start, end = 1, 10
l = []
flag = False
for j in range(1, len(d)+1):
    for i in range(0, len(d)):
        tmp = ''.join(map(str, d[i:i+j]))
        if len(tmp) > 1 and tmp[0] == '0':
            pass
        elif len(tmp) == j:
            l.append(int(tmp))
    l = sorted(set(l))
    if start == 1:
        for k in range(0, 10):
            if k not in l:
                print(k)
                flag = True
                break
    else:
        for k in range(start, end):
            if k not in l:
                print(k)
                flag = True
                break
    if flag:
        break
    start, end = start*10, end*10
    l = []

Fixed submission:
n = int(input())
length = int(n / 19) + 1
if n > 19 and n % 19 == 0:
    length -= 1
d = []
for i in range(length):
    d += list(map(int, input().split()))
start, end = 1, 10
l = []
flag = False
for j in range(1, len(d)+1):
    for i in range(0, len(d)):
        tmp = ''.join(map(str, d[i:i+j]))
        if len(tmp) > 1 and tmp[0] == '0':
            pass
        elif len(tmp) == j:
            l.append(int(tmp))
    l = sorted(set(l))
    if start == 1:
        for k in range(0, 10):
            if k not in l:
                print(k)
                flag = True
                break
    else:
        for k in range(start, end):
            if k not in l:
                print(k)
                flag = True
                break
    if flag:
        break
    start, end = start*10, end*10
    l = []

Buggy python submission (verdict: Runtime Error):
n = int(input())
length = int(n / 19) + 1 
d = []
for i in range(length):
    d += list(map(int, input().split()))

start, end = 1, 10
l = []
flag = False
for j in range(1, len(d)+1):
    for i in range(0, len(d)):
        tmp = ''.join(map(str, d[i:i+j]))
        if len(tmp) > 1 and tmp[0] == '0':
            pass
        elif len(tmp) == j:
            l.append(int(tmp))
    l = sorted(set(l))
    if start == 1:
        for k in range(0, 10):
            if k not in l:
                print(k)
                flag = True
                break
    else:
        for k in range(start, end):
            if k not in l:
                print(k)
                flag = True
                break
    if flag:
        break
    start, end = start*10, end*10
    l = []

Fixed submission:
n = int(input())
length = int(n / 19) + 1
if n > 19 and n % 19 == 0:
    length -= 1
d = []
for i in range(length):
    d += list(map(int, input().split()))
start, end = 1, 10
l = []
flag = False
for j in range(1, len(d)+1):
    for i in range(0, len(d)):
        tmp = ''.join(map(str, d[i:i+j]))
        if len(tmp) > 1 and tmp[0] == '0':
            pass
        elif len(tmp) == j:
            l.append(int(tmp))
    l = sorted(set(l))
    if start == 1:
        for k in range(0, 10):
            if k not in l:
                print(k)
                flag = True
                break
    else:
        for k in range(start, end):
            if k not in l:
                print(k)
                flag = True
                break
    if flag:
        break
    start, end = start*10, end*10
    l = []