N, M = map(int, input().split())

SC = []
if M == 0:
    if N > 1:
        print(10 ** N)
        exit()
    else:
        print(0)
        exit()

for _ in range(M):
    SC.append(tuple(map(int, input().split())))
SC = set(SC)

mem = []
ans = ['0'] * N
ans[0] = '1'
for idx, sc in enumerate(SC):
    if sc[0] in mem:
        print('-1')
        exit()

    mem.append(sc[0])
    ans[sc[0] - 1] = str(sc[1])

if len(ans) > 1:
    if ans[0] == '0':
        print('-1')
    else:
        print(''.join(ans))