n,m=map(int,input().split())
ans=[]

for i in range(m):
    ans.append(list(map(int,input().split())))
for j in range(10**n):
    if len(str(j))==n and all(str(j)[s-1]==str(c) for s,c in ans):
        print(j)
        break
else:
    print(-1)