求1-n以内所有偶数的和

&nbsp; <p class="MsoNormal"> <span style="font-family:宋体;font-size:12pt;">【题目描述】</span><span style="font-size:12pt;"></span> </p> <p class="MsoNormal"> <span style="font-size:12pt;"><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span><span>&nbsp;</span></span><span style="font-family:宋体;font-size:12pt;">给定一个正整数</span><span style="font-size:12pt;">N</span><span style="font-family:宋体;font-size:12pt;">，输出大于等于</span><span style="font-size:12pt;">1</span><span style="font-family:宋体;font-size:12pt;">且小于等于</span><span style="font-size:12pt;">N</span><span style="font-family:宋体;font-size:12pt;">的所有偶数的和</span><span style="font-size:12pt;"></span> </p> <p class="MsoNormal"> <span style="font-family:宋体;font-size:12pt;">【输入格式】</span><span style="font-size:12pt;"></span> </p> <p class="MsoNormal"> <span style="font-size:12pt;"><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span><span>&nbsp;</span></span><span style="font-family:宋体;font-size:12pt;">一个正整数，即</span><span style="font-size:12pt;">N</span> </p> <p class="MsoNormal"> <span style="font-family:宋体;font-size:12pt;">【输出格式】</span><span style="font-size:12pt;"></span> </p> <p class="MsoNormal"> <span style="font-size:12pt;"><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span><span>&nbsp;</span></span><span style="font-family:宋体;font-size:12pt;">仅包含一行，即答案</span><span style="font-size:12pt;"></span> </p> <p class="MsoNormal"> <span style="font-family:宋体;font-size:12pt;">【样例输入】</span><span style="font-size:12pt;"></span> </p> <p class="MsoNormal"> <span style="font-size:12pt;"><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span><span>&nbsp;</span>10</span> </p> <p class="MsoNormal"> <span style="font-family:宋体;font-size:12pt;">【样例输出】</span><span style="font-size:12pt;"></span> </p> <p style="text-indent:26.25pt;" class="MsoNormal"> <span style="font-size:12pt;">30</span> </p> <p class="MsoNormal"> <span style="font-family:宋体;font-size:12pt;">【数据规模】</span><span style="font-size:12pt;"></span> </p> <p style="text-indent:26.25pt;" class="MsoNormal"> <span style="font-size:12pt;">100%</span><span style="font-family:宋体;font-size:12pt;">的数据，</span><span style="font-family:宋体;font-size:12pt;">n</span><span style="font-family:宋体;font-size:12pt;">≤<span>10000</span></span> </p> <p class="MsoNormal"> <span style="font-family:宋体;font-size:12pt;">【样例解释】</span><span style="font-size:12pt;"></span> </p> <p class="MsoNormal"> <span style="font-size:12pt;"><span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span><span>&nbsp;</span>2+4+6+8+10=30</span> </p>