John 的数学成绩很差。老师给了他一项额外的任务。John 需要编写一个程序，计算从 $1$ 到 $n$ 的整数之和。如果他能提交一个正确的程序，他的差评将被取消。
编写一个程序，完成以下操作：
标准输入的第一行也是唯一一行包含一个整数 $n$ ($1 \le n \le 10\,000$)。
将一个整数写入标准输出。该整数应为从 $1$ 到 $n$ 的整数之和。
3
6
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