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题目描述

求 $4+7+10+13+16+...$， $n$个数的和。

输入格式

一个正整数 $n$。

输出格式

如题所述。

样例 #1

样例输入 #1

6

样例输出 #1

69

数据范围

$1 \le n \le 100000$