hotman78hotman78hotman78 is a Competitive Programmer and Waseda University student.2020-03-16T05:35:07.322ZTweetテストページtest ∑i=0ni=n(n+1)/2\sum_{i=0}^{n}i=n(n+1)/2∑i=0ni=n(n+1)/2-Like-CommentShareCopy linkShare on Twitter