import sys
n,m=map(int,input().split())
tmp=[-1]*n
for _ in range(m):
    s,c=map(int,input().split())
    s-=1
    if tmp[s]<0:
        tmp[s]=c
    if tmp[s]!=c:
        print(-1)
        sys.exit()
if tmp[0]==0 and n>1:
    print(-1)
    sys.exit()
if tmp[0]<0 and n>1:
    tmp[0]=1
if n==1 and tmp[0]==-1:
    tmp[0]=0
for i in range(1,n):
    if tmp[i]<0:
        tmp[i]=0
t=''.join(tmp)
print(t)