Buggy python submission (verdict: Runtime Error):
n,m=map(int, input().split())
r = []

for i in range(n):
    r.append(str(0))

if n != 1 and m == 0:
    print('-1')
    exit()

for i in range(m):
    s,c = map(int, input().split())
    if n == 1 and r[0] == '0':
        print('0')
        exit()
    elif n > 1 and s == 1 and c == 0:
        print('-1')
        exit()

    if int(r[s-1]) == 0:
        r[s-1] = str(c)
    elif int(r[s-1]) == c:
        r[s-1] = str(c)
    else:
        print('-1')
        exit()

if n > 1 and r[0] == '0':
    r[0] = 1
    print(''.join(r))
else:
    print(''.join(r))



Fixed submission:
n,m=map(int, input().split())
r = []

for i in range(n):
    r.append(str(0))

if n == 1 and m == 0:
    print('0')
    exit()
if n == 2 and m == 0:
    print('10')
    exit()
if n == 3 and m == 0:
    print('100')
    exit()

for i in range(m):
    s,c = map(int, input().split())
    if n == 1 and s == 1 and c == 0:
        print('0')
        exit()
    elif n > 1 and s == 1 and c == 0:
        print('-1')
        exit()

    if int(r[s-1]) == 0:
        r[s-1] = str(c)
    elif int(r[s-1]) == c:
        r[s-1] = str(c)
    else:
        print('-1')
        exit()

if n > 1 and r[0] == '0':
    r[0] = '1'
    print(''.join(r))
else:
    print(''.join(r))

Buggy python submission (verdict: Runtime Error):
n,m=map(int, input().split())
r = []

for i in range(n):
    r.append(str(0))

for i in range(m):
    s,c = map(int, input().split())
    if n > 1 and s ==1 and c == 0:
        print('-1')
        exit()

    if int(r[s-1]) == 0:
        r[s-1] = str(c)
    elif int(r[s-1]) == c:
        r[s-1] = str(c)
    else:
        print('-1')
        exit()
         
if n == 1 and r[0] == '0':
    print('0')
elif n > 1 and r[0] == '0':
    r[0] = 1
    print(''.join(r))
else:
    print(''.join(r))



Fixed submission:
n,m=map(int, input().split())
r = []

for i in range(n):
    r.append(str(0))

if n == 1 and m == 0:
    print('0')
    exit()
if n == 2 and m == 0:
    print('10')
    exit()
if n == 3 and m == 0:
    print('100')
    exit()

for i in range(m):
    s,c = map(int, input().split())
    if n == 1 and s == 1 and c == 0:
        print('0')
        exit()
    elif n > 1 and s == 1 and c == 0:
        print('-1')
        exit()

    if int(r[s-1]) == 0:
        r[s-1] = str(c)
    elif int(r[s-1]) == c:
        r[s-1] = str(c)
    else:
        print('-1')
        exit()

if n > 1 and r[0] == '0':
    r[0] = '1'
    print(''.join(r))
else:
    print(''.join(r))

Buggy python submission (verdict: Runtime Error):
n,m=map(int, input().split())
r = []

for i in range(m):
    r.append(str(0))

for i in range(m):
    s,c = map(int, input().split())
    if r[s-1] != '0' and int(r[s-1]) < c:
        r[s-1] = r[s-1]
    else:
        r[s-1] = str(c)
    
if m == 1 and r[0] == '0':
    print(0)
elif r[0] == '0':
    print('-1')
else:
    print(''.join(r))



Fixed submission:
n,m=map(int, input().split())
r = []

for i in range(n):
    r.append(str(0))

if n == 1 and m == 0:
    print('0')
    exit()
if n == 2 and m == 0:
    print('10')
    exit()
if n == 3 and m == 0:
    print('100')
    exit()

for i in range(m):
    s,c = map(int, input().split())
    if n == 1 and s == 1 and c == 0:
        print('0')
        exit()
    elif n > 1 and s == 1 and c == 0:
        print('-1')
        exit()

    if int(r[s-1]) == 0:
        r[s-1] = str(c)
    elif int(r[s-1]) == c:
        r[s-1] = str(c)
    else:
        print('-1')
        exit()

if n > 1 and r[0] == '0':
    r[0] = '1'
    print(''.join(r))
else:
    print(''.join(r))

Buggy python submission (verdict: Runtime Error):
n,m=map(int, input().split())
r = []

for i in range(m):
    r.append(str(0))

for i in range(m):
    s,c = map(int, input().split())
    r[s-1] = str(c)

if r[0] == '0':
    print('-1')
else:
    print(''.join(r))



Fixed submission:
n,m=map(int, input().split())
r = []

for i in range(n):
    r.append(str(0))

if n == 1 and m == 0:
    print('0')
    exit()
if n == 2 and m == 0:
    print('10')
    exit()
if n == 3 and m == 0:
    print('100')
    exit()

for i in range(m):
    s,c = map(int, input().split())
    if n == 1 and s == 1 and c == 0:
        print('0')
        exit()
    elif n > 1 and s == 1 and c == 0:
        print('-1')
        exit()

    if int(r[s-1]) == 0:
        r[s-1] = str(c)
    elif int(r[s-1]) == c:
        r[s-1] = str(c)
    else:
        print('-1')
        exit()

if n > 1 and r[0] == '0':
    r[0] = '1'
    print(''.join(r))
else:
    print(''.join(r))