N,M=map(int,input().split())
s=[0]*M
c=[0]*M
ans=[0]*N
s_1i=[]
s_2i=[]
s_3i=[]
for i in range(M):
    s[i],c[i]=map(int,input().split())
flg=0
for i in range(M):
    if s[i]==1 and c[i]==0:
        flg+=1
for i in range(M):
    if s[i]==1:
        s_1i.append(c[i])
    elif s[i]==2:
        s_2i.append(c[i])
    elif s[i]==3:
        s_3i.append(c[i])
if len(s_1i)>=2:
    if s_1i.count(s_1i[0])!=len(s_1i):
        flg+=1
if len(s_2i)>=2:
    if s_2i.count(s_2i[0])!=len(s_2i):
        flg+=1
if len(s_3i)>=2:
    if s_3i.count(s_3i[0])!=len(s_3i):
        flg+=1
if flg>=1:
    print("-1")
else:
    if (1 not in s) and (N!=1):
        ans[0]=1
    for i in range(M):
        ans[s[i]-1]=c[i]
    for i inrange(N):
        print(ans[i],end="")