import math

N, M = map(int,input().split())

if M == 0:
    print(10**(N-1))
else:
    s = list()
    c = list()
    for i in range(M):
        s_val, c_val = map(int, input().split())
        s.append(s_val)
        c.append(c_val)

    ans = 1000
    for i in range(int(10**(N)-1), int(10**(N-1)-1),-1):
        keta=list()
        for j in range(N):
            keta.append((math.floor(i/(10**j))%10))
        counter = 0
        for k in range(M):

            if keta[N-s[k]] == c[k]:
                counter += 1
            if counter == M:
                ans = i
    if ans == 1000:
        print(-1)
    else:
        print(ans)