Submission #1520236

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Source Code Expand

import java.util.Arrays;
import java.util.Scanner;

/**
 * http://abc026.contest.atcoder.jp/tasks/abc026_b
 */
public class Main {

	public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		final int N = sc.nextInt();
		int[] r = new int[N];
		for(int i=0; i<N; i++) r[i] = sc.nextInt();
		sc.close();
		
		Arrays.sort(r);
		double ans = 0;
		for(int i=N-1; i>=0; i--){
			int s = r[i]*r[i];
			ans = (N-i)%2==1 ? ans+s : ans-s; 
		}
		
		ans = ans*Math.PI;
		System.out.println(ans);
		
	}

}

Submission Info

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