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)
