给定圆的半径r求圆的面积

1 import java.util.*;
2 
3 public class Main {
4     public static void main(String[] args) {
5         Scanner scanner = new Scanner(System.in);
6         int r = scanner.nextInt();
7         System.out.printf("%.7f\n", Math.PI*r*r);
8     }
9 }