n, m = map(int, input().split())
sc = [list(map(int, input().split())) for _ in range(m)]
def f():
    for i in range(1000):
        x = str(i)
        if len(x) == n:
            cnt = 0
            for j in range(m):
                if sc[j][0] > n:
                    break
                elif sc[j][0] <= n:
                    if x[sc[j][0] - 1] == str(sc[j][1]):
                        cnt += 1
                        if cnt == m:
                            return x
                    elif x[sc[j][0] - 1] != str(sc[j][1]):
                        break
    return -1
print(f())