一条长廊里依次装有n(1 ≤ n ≤ 65535)盏电灯，从头到尾编号1、2、3、…n-1、n。每盏电灯由一个拉线开关控制。开始，电灯全部关着。

有n个学生从长廊穿过。第一个学生把号码凡是1的倍数的电灯的开关拉一下；接着第二个学生把号码凡是2的倍数的电灯的开关拉一下；接着第三个学生把号码凡是3的倍数的电灯的开关拉一下；如此继续下去，最后第n个学生把号码凡是n的倍数的电灯的开关拉一下。n个学生按此规定走完后，长廊里电灯有几盏亮着。

注：电灯数和学生数一致。-A corridor in turn fitted n (1 ≤ n ≤ 65535) light bulb, from start to finish No. 1,2,3, ... n-1, n. Each light bulb controlled by a pull switch. Start, lights all closed. There are n number of students from across the promenade. The number of students who first light switch in multiples of 1 pull　then the number of students who second light switch pull multiple of 2　then a third of the number of students who multiples of three light switches pull　case continues, the last n-th number of students who light switch to a multiple of n pull. n After a student has completed this provision, there Jizhan lamp lit corridor. Note: The number of students and the number of lamps in line.