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


def answer():
    digs = [-1] * N
    for _ in range(M):
        s, c = map(int, input().split())
        s -= 1
        if s == 0 and c == 0:
            return -1
        if digs[s] not in {c, -1}:
            return -1
        digs[s] = c
    if digs[0] == -1:
        digs[0] = 1
    if digs[1] == -1:
        digs[1] = 0
    if digs[2] == -1:
        digs[2] = 0
    return "".join(map(str, digs))


print(answer())
