N,M=map(int, input().split())
SC=[list(map(int, input().split())) for _ in range(M)]
for i in range(1000):
	count=0
	if len(str(i))==N:
		for sc in SC:
			s,c=sc[0],sc[1]
			if s==1 and i//(100)==c and c!=0:
				count+=1
			if s==2 and len(str(i))==2:
				if int(str(i)[0])==c and c!=0:
					count+=1
			if s==2 and len(str(i))==3:
				if int(str(i)[1])==c:
					count+=1
			if s==3 and i%10==c:
				count+=1
			else:
				continue
		#print(i,count)
		if count==len(SC):
			print(i)
			exit()

print(-1)

