https://www.acmicpc.net/problem/19242
https://www.acmicpc.net/problem/1606
https://www.acmicpc.net/problem/17464
https://www.acmicpc.net/problem/19651
https://www.acmicpc.net/problem/12928
https://www.acmicpc.net/problem/20541
https://www.acmicpc.net/problem/20297
https://www.acmicpc.net/problem/19851
https://www.acmicpc.net/problem/19650