N,M = input().split()
s,c,a = [],[],[]
number = []
for i in range(int(M)):
    a_i = input().split()
    a.append(a_i)
    s.append(int(a_i[0]))
    c.append(int(a_i[1]))
ans = True
for i in range(int(N)):
    number.append('')
for i in range(int(M)):
    if s[i]==1 and c[i]==0 and int(N)>1:
        if ans:
            print('-1')
            ans = False
    elif number[s[i]-1] == '' or number[s[i]-1] == c[i]:
        number[s[i]-1] = c[i]
    else:
        if ans:
            print('-1')
            ans = False
for i,elem in enumerate(number):
    if number[i] == '' and i == 0:
        number[i] = 1
    elif elem == '':
        number[i] = 0
if ans:
    strs = '' 
    for i in number:
        strs += str(i)
    print(int(strs))