def main():
    n, m = map(int, input().split())
    ans = [None]*n
    for _ in range(m):
        s, c = map(int, input().split())
        try:
            if ans[s-1] is None:
                if c == 0 and s != n:
                    print("-1")
                    return
                ans[s-1] = c
            elif ans[s-1] != c:
                print("-1")
                return
        except:
            print("-1")
            return
    ans_str = ""
    p = ans.pop(0)
    if p is None:
        ans_str += "1"
    else:
        ans_str += str(p)
    if ans:
        for a in ans:
            ans_str += str(a) if a else "0"
    print(ans_str)


if __name__ == "__main__":
    main()