计算n以内的质数个数。（由于文件小于1kb，禁止上传，所以就复制了几个副本） 采用欧拉算法，运行速度极快，100000000以内的数字，只要几毫秒就可得出结果-Calculate the number of quality within the number n. (Because the file is less than 1kb, prohibit the uploading, so I copied several copies) Euler algorithm, run fast,