题解 | #牛牛学圆#

import java.text.DecimalFormat;
import java.util.Scanner;

public class Main {
public static void main(String[]args){
Scanner sc = new Scanner(System.in);
double a = sc.nextDouble();//实数用double来接
double pi = 3.14159;
double perimeter = 2pia;
double area = piaa;
DecimalFormat df = new DecimalFormat("0.000000");
System.out.println(df.format(perimeter));
System.out.println(df.format(area));

 }     

}