n,m=map(int,input().split())
s,c=[],[]

for _ in range(m):
    a,b=map(int,input().split())
    a-=1
    s.append(a)
    c.append(b)
        
for ans in range(10**(n-1),10**n):
    st=str(ans)
    f=True    
    for i in range(m):
       if st[s[i]] != str(c[i]):
            f=False
          
    if f==True:
        print(ans)
        exit()

print(-1)