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

for i in range(10**N):
    scstr = str(i)

    if len(scstr) == N and all(scstr[s-1] == str(c) for s,c in sc):
        print(i)
        break
else:
    print(-1)


