N,M=map(int,input().split())
li=[0]*n
for i in range(M):
    si,ci=map(int,input().split())
    if li[si-1] != 0 and li[si-1] !=ci:
        print(-1)
        exit(0)
    if si==1 and ci==0:
        if N>1:
            print(-1)
            exit(0)
    li[si-1]=ci
if N>1 and li[0]==0:
    li[0]=1
for i in range(N):
    print(li[i],end="")
