n,m=map(int,input().split())
a=['.']
a*=n
ans=0
for i in range(m):
    si,ci=input().split()
    si=int(si)
    ci=str(ci)
    if a[si-1]=='.':
        a[si-1]=ci
    else:
        if a[si-1]==ci:
            continue
        else:
            ans=-1
            break

if ans==-1 or (n>=2 and a[0]=='0'):
    print(-1)
else:
    if n==1 and a[0]=='.':
        a[0]=0
    elif a[0]=='.':
        a[0]='1'
    for i in range(1,n):
        if a[i]=='.':
            a[i]='0'
    a=''.join(a)
    print(a)