def main():
    n, m = map(int, input().split())
    ans = [-1]*n
    for _ in range(m):
        s, c = map(int, input().split())
        if ans[s-1] == -1:
            ans[s-1] = c
        elif ans[s-1] != -1 and ans[s-1] != c:
            print(-1)
            exit()

    if n == 1:
        if ans[0] == -1:
            ans[0] = 0
    else:
        if ans[0] == -1:
            print(-1)
            exit()

        if ans[0] == -1:
            ans[0] = 1

        for i in range(1, n):
            if ans[i] == -1:
                ans[i] = 0
    print(*ans, sep="")


if __name__ == "__main__":
    main()
