n, m = list(map(int, input().split()))

    
out = ['a']*n
err_flg = False
err_flg2 = False 

for i in range(m):
    s = list(map(int, input().split()))

    if s[0]==1 and s[1]==0 and n > 1:
        err_flag = True
    elif s[0]==1 and s[1]==0 and n==1:
        err_flg2 = True
    elif m==0 and n==1:
        err_flg2 = True

    if out[s[0]-1]=='a':
        out[s[0]-1] = s[1]
    elif out[s[0]-1]==s[1]:
        out[s[0]-1] = s[1]
    # elif out[s[0]-1]!=s[1]:
    elif out[s[0]-1]!=s[1]:
        err_flg = True


if out[0]=='a' and n>1:
    out[0]=1
    

out_s = "".join(map(str,out))


if err_flg:
    print('-1')
# elif m==0 and n==1:
#     print(0)
elif err_flg2:
    print('0')
else:
    print(out_s.replace('a','0'))