n,m=map(int,input().split())
L=[10]*n
for i in range(m):
    s,c=map(int,input().split())
    if L[s-1]!=10:
        if L[s-1]!=c:
            print(-1)
            exit()
    else:
        L[s-1]=c
if n==1:
    if L[0]==10:
        print(-1)
        exit()
else:
    if L[0]==10 or L[0]==0:
        print(-1)
        exit()
    else:
        for i in range(n-1):
            if L[i+1]==10:
                L[i+1]=0
print(''.join(map(str,L)))