import java.util.Scanner;
public class Main {
public static void main(String[] args) {
//S=PI*R*R
Scanner in = new Scanner(System.in);
java.text.DecimalFormat df=new java.text.DecimalFormat("#.0000000");
int r = in.nextInt();
double s = Math.PI * r * r;
System.out.println(df.format(s));
}
}
原文：http://www.cnblogs.com/LuckyZcy/p/5163943.html