n,m=map(int,input().split())
l=["0"]*n
l[0]="1"
f=[0]*n
frag=0
for i in range(m):
    s,c=map(int,input().split())
    if f[s-1]==0 or l[s-1]==str(c):
        l[s-1]=str(c)
        f[s-1]=1
    else:
        frag=1
        break
if frag==1 or (l[0]=="0" and n!=1):
    print(-1)
else:
    for j in l:
        print(j,end="")