N, M = map(int, input().split())
s = []
c = []
for m in range(M):
    si, ci = map(int, input().split())
    s.append(si)
    c.append(ci)

s = 10 ** (N - 1)
if N == 1:
    s -= 1

for i in range(s, 10 ** N):
    for m in range(M):
        if str(i)[s[m] - 1] != str(c[m]):
            break
    else:
        print(i)
        exit()

print(-1)
