N, M = map(int, input().split())
s = []
c = []
for i in range(M):
    s_i, c_i = map(int, input().split())
    s.append(s_i)
    c.append(c_i)
for i in range(10**(N-1), 10**N):
    for j in range(M):
        if str(i)[s[j]-1] != str(c[j]):
            break
        if j == M - 1:
            print(i)
            c = 1
            break
    if c == 1:
        break
    if i == 10**N -1:
        print(-1)