judge = False
target = [-1 for i in range(N)]
for i in range(M):
    if sc[i][1] + target[sc[i][0]-1] == sc[i][1]-1 or sc[i][1] + target[sc[i][0]-1] == 2*sc[i][1]:
        target[sc[i][0]-1] = sc[i][1]
    else:
        print(-1)
        judge = True
        break

if judge is False:
    for i in range(N):
        if len(target) == 1:
            if target[0] == -1:
                target[0] = 0
        else:
            if i == 0 and target[i] == -1:
                target[i] = 1
            elif target[i] == -1:
                target[i] = 0

    res = 0
    for i in range(N):
        res = res+target[i]*(10**(N-i-1))
    if len(str(res)) != N:
        print(-1)
    else:
        print(res)