N, M = map(int, input().split())
sc = [tuple(map(int, input().split())) for _ in range(M)]

for i in range(1000):
    t = str(i)
    if t != N:
        continue
    ok = True
    for s, c in sc:
        if t[int(s)] != int(c):
            ok = False
            break
    if ok:
        print(i)
        exit()
print(-1)
