n, m = map(int, input().split())
sl = list(list(map(int, input().split())) for _ in range(m))
# print(sl)
sl = list(map(list, set(map(tuple, sl))))
# print(sl)

cnt = [0]*n
cnn = [-1]*n
for s in sl:
    if cnt[s[0]-1] == 0:
        cnt[s[0]-1] += 1
    else:
        print(-1)
        exit()

if n != 0:
    num = list(str('1'+'0'*(n-1)))
    for s in sl:
        if s[1] == 0:
            print(-1)
            exit()
        # elif num[s[0]-1] != 1 and num[s[0]-1] != '0':
        #     print(-1)
        #     exit()
        elif num[s[0]-1] != str(s[1]):
            num[s[0]-1] = str(s[1])
            # if num > _num:
            #     num = _num
    print(*num, sep='')
else:
    print(0)
    

