n, m = map(int, input().split())
sc = [list(map(int, input().split())) for i in range(m)]
sc = list(map(list, set(map(tuple, sc))))

ans = [-1] * n
for i in sc:
    if i[0] == 1 and i[1] == 0:
        print(-1)
        exit()
    if i[0] > n or ans[i[0]-1] != -1:
        print(-1)
        exit()
    ans[i[0]-1] = i[1]

for i, val in enumerate(ans):
    if val == -1:
        ans[i] = 0

if (m == 0 and n != 1) or (ans[0] == 0 and n != 1):
    ans[0] = 1

flg = False
for i in ans:
    if i != 0:
        flg = True
if not flg:
    print(0)
    exit()

ans = map(lambda x: str(x), ans)
print("".join(ans))