【Codeforces Round #501 (Div. 3)】
A:https://www.cnblogs.com/myx12345/p/9842904.html
B:https://www.cnblogs.com/myx12345/p/9842964.html
C:https://www.cnblogs.com/myx12345/p/9842977.html
D:https://www.cnblogs.com/myx12345/p/9852909.html
E:https://www.cnblogs.com/myx12345/p/9932309.html
F:https://www.cnblogs.com/myx12345/p/9935872.html
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