N, M = map(int, input().split())
ans = {}
flg = False
for _ in range(M):
    s, c = map(int, input().split())
    if s == 1 and c == 0:
        if N == 1:
            flg = True
        else:
            print(-1)
            exit()
    else:
        if s in ans.keys():
            if c != ans[s]:
                print(-1)
                exit()
        else:
            ans[s] = c
if flg:
    print(0)
else:
    num = ["1"] + ["0"]*(N-1)
    for k, v in ans.items():
        num[k-1] = str(v)
    print("".join(num))
