n, m = map(int, input().split())
req = [list(map(int, input().split())) for i in range(m)]
for i in range(10000):
    st = str(i)
    if len(st) != n:
        continue
    ok = True
    for s, c in req:
        if int(st[s-1]) != int(c):
            ok = False
    if ok:
        print(st)
        exit(0)

print(-1)