why the qauthor of today's div2-912 round use the same idea of an old problem ↵
↵
↵
to day's problem : ↵
[https://codeforces.me/contest/1903/problem/C](https://codeforces.me/contest/1903/problem/C)↵
↵
the old problem : ↵
[https://codeforces.me/contest/1175/problem/D](https://codeforces.me/contest/1175/problem/D)
↵
↵
to day's problem : ↵
[https://codeforces.me/contest/1903/problem/C](https://codeforces.me/contest/1903/problem/C)↵
↵
the old problem : ↵
[https://codeforces.me/contest/1175/problem/D](https://codeforces.me/contest/1175/problem/D)