N, M = map(int, input().split())
lst = [0] * N
if M == 0 and N != 1:
    lst[0] = 1
else:
    dic = {}
    for _ in range(M):
        s, c = map(int, input().split())
        n = dic.get(s)
        if n is not None and n != c:
            print(-1)
            exit()
        dic[s] = c

if N != 1 and lst[0] == 0:
    print(-1)
    exit()

for k, v in dic.items():
    lst[k - 1] = v

if len(lst) != 0 and lst[0] == 0:
    lst[0] = 1

print("".join(map(str, lst)))
