import java.util.Scanner; public class Main{ public static void main(String []args){ Scanner sc = new Scanner(System.in); int n = sc.nextInt(); double sum = 0; int temp2 = 0; for(int i = 1; i <= n; i++){ int temp1 = 0; if(i % 2 == 0){ temp1 = -(i * 2 - 1); }else{ temp1 = i * 2 - 1; } temp2 = temp2 + temp1; sum = sum + 1.0 / temp2; } System.out.printf("%.3f",sum); } }这题我用了两个变量来存储值,第一个计算该加分母的大小,第二个计算分母之和。