n, m = map(int, input().split())
lst = [x for x in range(n)]
dic = {}
not_found = False
special_case = False
for i in range(m):
    a, b = map(int, input().split())
    if str(a) not in list(dic.keys()):
        dic[str(a)] = b
    else:
        if dic[str(a)] != b:
            not_found = True
    lst[a - 1] = b
if m == 0 and n != 1:
    not_found = True
if m == 0 and n == 1:
    special_case = True
if not_found:
    print(-1)
elif special_case:
    print(0)
else:
    for i in range(n):
        if str(i + 1) not in list(dic.keys()):
            if i + 1 == 1:
                lst[i] = 1
            else:
                lst[i] = 0
    lst = list(map(str, lst))
    res = ''.join(lst)
    if res[0] == '0' and len(res) > 1:
        print(-1)
    else:
        print(int(res))