N, M = map(int, input().split())
ans = [-1 for _ in range(N)]
for _ in range(M):
    s, c = map(int, input().split())

    if ans[s - 1] == -1 or ans[s - 1] == c:
        ans[s - 1] = c
    else:
        print(-1)
        exit()


if N != 1 and ans[0] == 0:
    print(-1)
    exit()


for i in range(N):
    if ans[i] == -1:
        if i == 0:
            ans[i] = 1
        else:
            ans[i] = 0

print(''.join([str(s) for s in ans]))
